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23. STROPHIA DALLII Novo.
Dall's Strophia.
Plate XIII, 23 & 23a, shell. Fig. 32, front, A, transverse section: 0, upper, terminal portion of channeled tooth; c, frontal bar; e, channeled tooth, enlarged. FIG. 33, left side.
DESCRIPTION.
Sp. Ch. Size, rather large. Shell, heavy. Striations, present. Whirls, 10. Teeth, two, the upper inconspicuous, the lower extremely long and channeled. Examined 25 specimens.
Form of shell, cylindrical, with the first three whirls of the same diameter, the fourth is but little smaller, and from this the shell slopes to a rather blunt point,, forming an angle of 60 degrees. The sutures are very shallow, and the whirls between them bulge but little
The striations are very numerous, 50 on the first whirl, are not arranged in lines, yet are quite regular; they are slightly inclined from right to left. and the interspaces are a little narrower than the prominences. The striations are rounded on top and polished.
Aperture quite large and open, but narrows rather rapidly within.
The lower tooth is not very prominent, but extending backward along the lower wall about .15, becomes widened and channeled, and in this form passes downward, terminating on the right side of the third whirl; its length is thus about .75! Its position is a little nearer the column which it encircles, than to the outer wall. (See Fig. 32, A, where is given a life size view of the upper portion of the tooth, the top of the shell having been removed; 0, shows the tooth; c the frontal bar.) The upper tooth is a mere prominence, but gains in size as it passes backward, and makes a complete turn around the column.
The margin is not produced forward beyond the diameter of the shell, slopes slightly backward, and is a very little inclined to the right, is rather thick, measuring .06, and the edge is rolled slightly backward, but is not thin. Frontal bar, well developed, and the lower wall of the aperture within it is smooth, but the striations are slightly apparent beneath the enameling.
Color of shell, externally, shining white, sparingly mottled with reddish, but more prominently on the smaller whirls. The outer margin is white, but within, there being an abrupt line of demarkation, it is dark purplish brown.
DIMENSIONS.
Size of type, 1.20 by .42. Largest specimen, 1.22 by .45, smallest, 1.18 by .40. Greatest diameter, .45; smallest, .40. Largest specimen, 1. 22; smallest, 1.18.
OBSERVATIONS
Specimens do not vary essentially from the type. This is a remarkable shell. In it we find the maximum number of striations, no other known species having so many. It may be considered the type of a group of Strophias having the peculiar channeled, greatly elongated tooth. These, as far as my present knowledge extends, are confined to the island of Inagua, where all of the species of Strophia are thus characterized.
By the teeth alone, the Strophias may be divided into at least four sharply defined groups, as follows:-
LOWER TOOTH, GREATLY ELONGATED, CHANNELED; POSITION, CENTRAL.
Lower tooth, projected backward along the lower wall, at least beyond the first whirl and channeled excepting on upper termination. (See Fig. 32, A, where is given the upper termination of the channeled tooth of S. dallii; 0, being the tooth and c, the frontal bar; e is the upper termination greatly enlarged, showing beginning of channel. At Fig. 33, A, is the lower termination of the tooth of S, pallida.) Habiitat of species, Inagua, Bahamas. Type, S. dallii.
LOWER TOOTH, ELONGATED, SIMPLE; POsrfION, CENTRAL.
Lower tooth, projected back into the aperture for a distance at least four times its height, but it is not channeled, being a simple pyramid. (See Plate II, lc, where a side view of the elongated central tooth of S. pannosa is given; in Fig. 33, a top view of the same is represented; at ib. c, is given the top of that of S. copia; the top of that of S. nana is figured at ib. i.) Habitat of species, the Cayman Islands. Type, S. pannosa.
LOWER TOOTH, SHORT; SIMPLE; POSITION, CENTRAL.
Lower tooth, short, its length being no more than three times its height, and its position is about central. ( See Plate VII, 17b, where is given a side view of the short tooth of S. alba, and Fig. 33, b, where is represented the top of the tooth of S. neglecta.) Habitat of species, Bahamas. -excepting Inagua ? Cuba, and probably Hayti. Type, S. neglecta.
LOWER TOOTH, SHORT; SIMPLE; POSITION, NOT CENTRAL.
Lower tooth. very short, its length being no more than twice its height, but its position is considerably to the right of the center, being, in fact, placed nearly on the column. (See Fig. 34, A, where is given an enlarged cut of the teeth. lower and upper, of S. uva, showing the near proximity of the two, and the position of the lower, almost on the column.) I cannot at present clearly define the habitat of the species of this group. It is, however, safe to say that they are found on the more northern of the Windward Islands, and some of the keys off the north coast of South America ?Curacoa and vicinity. Type, S. uva.
[NOTE. The material examined upon which the foregoing conclusions are based. consists of at least three fourths of the known species of Strophia. Of course among the large amount of fresh material to be gathered, for without doubt, nearly every island among the Bahamas and other West Indies, not yet explored for Strophias, will yield one or more species. forms may occur that will, perhaps, cause me to modify my ideas somewhat, but I have considered it best to give this exposition of my studies upon the group up to date, in order that students may better understand my descriptions. Further remarks upon this head will be given under General Conclusions.]
An understanding of these groups, as defined, is of great importance in determining species in Strophia. Of course, other characters are often constantly found in a given group. For example, the Inagua Strophias, having the channeled tooth, are nearly always cylindrical, the the first three whirls being about equal in diameter, while the striations are fine and numerous. Both of these characters are also found in the short toothed group, but here they are not constant, nor do they always occur together. Other groups possess other characters, to be mentioned elsewhere. In fact, it is nearly always possible to find species in one group that bear a superficial resemblance to others in different groups, when they are really utterly different.
The sharply defined difference in the teeth, as pointed out, becomes of more importance when we consider that specific characters are much less prominent in Strophia than in many other genera of shells, although as constant as those more easily perceived. Thus these groups become, in a measure, sub-generic.
It is a well known fact that in some genera, or even families, in all classes of animals, species are much more closely allied than in others, and that certain characters are constant in some genera, thus are available in defining species, which are inconstant and thus valueless for this purpose in others.
Any naturalist, not narrowed down to a specialty, will acknowledge the truth of the above made statement, as his attention must be constantly called to it in his investigations.
Again, we must acknowledge that groups of animals in which species are not readily defined, require the closest study in order to clearly understand just what characters are of value in deciding specific rank.
The genus Strophia presents one of these very problems, and whether from the difficulty of recognizing species, or from some other cause, has been strangely neglected, as I have had occasion to remark many times, by naturalists on this side of the Atlantic. It is true that there is quite an extensive literature upon Strophia in connection with Pupa, but very much of this is valueless on account of too great generalization in describing species. Then again, two, or more, species are often included under one name, consequently descriptions become very confusing.
I may appear to be making a sweeping statement here, but am sure that I am correct in this assertion. As proof of this I have only to bring forward the fact that in some of the largest collections in the country, that have been examined by me, names are applied to comparatively few species, and when applied are often obviously wrong, as the same name is, in many cases, appended to more than one species, while, on the other hand, instances are not wanting where the same species has received different names!
Now I do not pretend that I have done any more than anyone can do in the study of Strophia, who has modern ideas regarding species and the requisite training. But I have given the subject very much attention and thought. It is true, that I have much to learn, for there is a broad field still before me, but as far as I have been the matter appears perfectly clear to me.
I cannot help feeling that many conchologists, at least in America, are unfamiliar with this genus through prehaps having neglected it as of not sufficient importance to warrant the application and thought that the subject merits. I may say, however, that since the appearance of the first number of my monograph, I have met with much kindness, as well as encouragement, from many prominent naturalists who have aided me in many ways in prosecuting my researches.
I wish to emphasize the assertion made before, that no one species of Strophia, with rare exceptions, is found on different islands, unless recently transported by commercial intercourse. Two instances where this has occurred, are in S. copia and S. intermedia, and I must now record another. Among the Strophias belonging to the Smithsonian Institute are a lot of undoubted S. inflata, labelled as coming from Exuma, the type being from the Bryant collection, taken at Salina Point, Auklin Island, 100 miles distant.
Of course in making the above written statement I do not wish to be understood to say that simple geographical bounderies constitute specific rank. As shown in many instances, Strophia is an exceedingly plastic genus; that is, for some reason, now beyond our knowledge, species become evolved quite readily and in conformity with a law of evolution, most readily toward the center of the greatest distribution of the species. Hence it is, that if by any chance, some members of a species become isolated, either by being transported to a separate island, or to some section of the same island where they are isolated by the surroundings, and as pointed out already under the habits of S. nana, comparatively little is necessary to so isolate them, they are apt to speedily assume specific characters. This is, prehaps, caused by different environment, different food, or possibly wholly by an inherent tendency to vary from the parent stock.
As shown, especially under observations in S. copia, there is a great tendency to assume forms, under apparently the same environment, and these forms generally indicate the specific characters that will be assumed by isolated individuals. For example, I find that among a large series of S. incana from Key West, some few individuals which show faint indications of brown fleckings, and Dr. Dall writes me that in the Smithsonian collection are specimens of undoubted S. incana that are flecked. Now this is exactly what I should expect to see, for it is in perfect accordance with the law of evolution of which I have been speaking, and clearly indicates the flecked S. fasciata found at Key Vaccas.
Now through the operations of the well known law of reversion, (a law too much ignored by naturalists practically, although generally recognized by them,) individuals among nearly all species, especially if recently evolved, will show a tendency to revert toward the parent stock; this is eminently true in Strophia, and to this cause, in connection with the foreshadowing of species, explained above, is due much of the apparent confusion in many species which are closely allied, but really distinct.
In studying Strophia, I have always endeavored to first thoroughly understand the intricacies of the oscillations of individual variation, -greater in some species than in others-then have indicated the more or less set forms that have passed beyond mere individual variation, but which have not lost the links that bind them to the parent stock; thus have been prepared to recognize species, even if closely allied, wherein there are no true connecting links.
In concluding this digression, which I have considered necessary to make at this time, I shall recapitulate somewhat in the following remarks, in order to emphasize some of my assertions.
The genus Strophia is larger and much more important than has been supposed. On this side of the Atlantic, at least, it has been much neglected, and consequently many collections are in a sad state of confusion regarding proper names being appended to species. Many easily recognized species have received the same name, and the same species sometimes bear different names in the same collection, (in one instance two lots of one species labelled as coming from one locality, have received different names, both of which are in the same handwriting!) while in many cases the same species bears different names in different collections. Much of this confusion is due to the fact that, with a few exceptions, writers upon Strophia, especially the older authors, have not given enough attention to details, hence one description often embraces more than one species. They have scarcely ever recognized the importance of isolation as indicating species, and are thus apt to assign too wide a range to one species.
Many students of today in endeavoring to identify species by these descriptions have tried to make too few names fit too many species, and through an unfamiliarity with the subject, have not observed their error.
Indvidual variation is sometimes comparatively great in species of Strophia, yet this has its limits, becoming overbalanced into forms, and these, in turn, into species. A tendency to indicate the species that has been evolved through the isolation of individuals, by a greater or less prominence of some particular character, on one hand, and reversion in some specimens of that recently evolved species, will sometimes form what are apparently connecting links between the two species. Such apparent links are, however, always represented by a very small percentage of specimens, and a close study of them, will, in all cases, show to which species each belongs. Strophia, to be understood, requires careful study and attention, more so than most genera of shells, but when once mastered, certain characters that before seemed obscure, now become perfectly clear.
In making the foregoing remarks, I have frankly and freely stated the conclusions to which I have come, after a long and most careful consideration of the subject, my sole object being the advancement of our knowledge of the genus Strophia. If I differ in opinion from some authors whose descriptions I have considered too general, it is not because I do not appreciate their labors, but rather because I take a different view of the matter from what they then took. I thoroughly believe that the time has come when the utmost minuteness of detail has become necessary in defining groups in nature, of whatever grade, but more especially is such minuteness of description needful in working out the details of specific and subspecific characters.
It must be constantly borne in mind that we of today are working as much, if not more, for the benefit of the coming generations as for that of the present. He who is a student of evolution must admit constant change, and to him it becomes most obvious that too careful attention cannot be given to minute differences in recording the present condition of the species or subspecies in hand, as thus, and only thus, can our work be available in the future to those who wish to mark the steps of change.
I do not intend to be understood that I would for a moment think of recording differences in Strophia which are not constant and of sufficient specific importance to warrent so doing, and I am sure that I have not done so, as I feel confident that no one who will give the matter the careful attention that it merits, will disagree with me.
Strophia dallii may be known by the numerous striations-more than in any other described species-the cylindrical form, and channeled tooth. I have dedicated this species to the accomplished naturalists, Dr. William H. Dall, curator of mollusks at the Smithsonian Institute, Washington, D. C., as a slight testimonial of my appreciation of the value of his scientific researches.
Among the channeled toothed Strophias should be included the previously described S. ianthina and S. pallida.
DISTRIBUTION AND HABITS.
The first specimen of Dall's Strophia that I ever saw, I found in my Bahama collection of shells, but unfortunately labelled so that it was uncertain whether it came from Inagua or not. Later I found a few of this species in the collection of Mr. James A. Southwick, but again I was unfortunate in not getting the locality. It was only upon receiving a series of the Smithsonian Strophias, kindly forwarded to me by Dr. Dall, that I found the species labelled as coming from Inagua." Maynard, 1889:128-135).
