"Original Description:  "Shell cylindrical, robust, finely and rimately umbilicated, and axially costate.  Whorls 8½ to 9 and but slightly convex.  Color almost china-white and slightly shining.  Spire convexly conic above the sixth whorl, remaining whorls nearly straight sided.  Spire cast at an angle of about 65°.  Aperture subcircular with the lip reflected and bur slightly turned back.  Parietal tooth rather large and well developed.  Parietal ridge hardly expressed byond the usual glaze.  Suture well indicated but very shallow.  Sculpture of numerous and well developed axial costae, numbering 19 on the body whorl (holotype). The nuclear whorls are also sculptured with very fine and exceedingly numerous axial riblets. 

            Length             Width               Aperture

            22.5                 9.6                   7.   x 6.2 mm    Holotype  [fig. 7]

            22.5                 10.                   7.1 x 5.5 mm    Paratype

            21.8                 10.                   6.8 x 6.   mm    Paratype

            23.2                 11.                   7.   x 6.   mm    Paratype

Type Locality:  Mono Island, Puerto Rico. H. A. Beatty coll. 1944.

Type Material:  Holotype, MCZ 171019. "Paratypes from the same locality.  Additional paratypes from Isabella Anchorage, collected by P. Bartsch in 1933.

Holotype measurements:  Length mm, diameter (excluding lip) mm; aperture height (including lip) mm, aperture width (including lip and peristome) mm.

Remarks:  "This species appears to be nearest in its relationship to Cerion yumaense Pilsbry and Vanatta from Saona Island off the southeast coast of Hispaniola.  C. monaense is larger, has white nuclear whorls rather than buff and has far less mottling.  In all other characters they are exceedingly close.  From Cerion striatellum Guerin of Puerto Rico, C. monaense differs by being smaller and having much coarser costae."

            Thompson (1987:83) surveyed the land snails of Mona Island and reported Cerion monaensis Clench to be abundant and generally distributed on the coastal plains along the south side of Mona Island.  Locally distributed on the limestone plateau." (Clench, 1951:274)