THE CYCI.OPH0RID LAND M0LLUSK9 OF AMERICA 125 



Cycladamsia, new subgenus 



Shells of this subgenus resemble Neocyclotus in shape and general 

 sculpture of shell but differ in having a keel at the exterior limit of 

 the umbilicus. Operculum covered on the outside with a thick cal- 

 careous deposit, which forms a weak ridge on the inner edge of the 

 whorls and tapers outwardly, its surface being obliquely striated. 



Type: Cyclostoma seminudum C. B. Adams = Aperostoma {Cycla- 

 damsia) seminudum (C. B. Adams). 



The subgenus Cycladamsia appears confined to a strip of western 

 Jamaica lying between longtitude 77° 30' and 78° W. and latitude 18° 

 and 18°25' N., except for two crab-carried specimens from Montego 

 Bay, which is a little farther north. 



The radula of Aperostoma (Cycladamsia) seminudum seminudum 

 (C. B. Adams) and A. (C.) seminuduTn scahratwm have the formula 

 3:3:3:3, and the jaw without median projection. 



KEY TO THE SPECIES OF SUBGENUS CYCLADAMSIA 



Whorls strongly pitted or malleated. 



Last fourth of base of last whorl with regular oblique ridges. 



Oblique ridges extending from umbilical keel to periphery ruber 



Oblique ridges not extending from umbilical keel to periph- 

 ery bairdianum 



Last fourth of base of last whorl without regular oblique ridges. 



Shell large, greater diameter more than 23 mm seminudum 



Shell smaller, greater diameter less than 20 mm fossile 



Whorls not strongly pitted or malleated ., rudisplanusque 



APEROSTOMA (CYCLADAMSIA) RUBER (Chitty) 



Shell helicoid. Nuclear whorls 1.3, small, well rounded, smooth ; the 

 first half postnuclear whorl with slender, retractively curved axial 

 riblets, which are separted by spaces about as wide as the riblets. 

 This stage is followed by a turn in which the axial sculpture becomes 

 irregular and the ribs obsolete, then by a wrinkled and pitted stage 

 that continues to the end of the last whorl. In the early portion of 

 this stage the wrinkles are more or less regular and decidedly retrac- 

 tively curved. They are not of uniform development, which condi- 

 tion gives the spaces between the wrinkles a pitted aspect. The 

 summit of the whorls is appressed; the suture is not impressed. 

 Periphery well rounded. Base well rounded, openly umbilicated, 

 the umbilicus marked by a strong cord at its outer termination. 

 The cord within the umbilicus is pinched in. The sculpture of the 

 base consists of decidedly obliquely retractively curved cords, which 

 are wavy and feebly nodulose, enclosing spaces of a little less width 

 between them, which have a somewhat pitted aspect. The umbilical 



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