72 BULLETIN 192, UNITED STATES NATIONAL MUSEUM 



operculum closes the shell may be present or absent. They show an 

 enormous range of specialized development, which will be discussed 

 under each genus. 



Type genus: Rhytidopoma Sykes. 



KEY TO THE HISPANIOLAN GENERA OF THE SUBFAMILY nHYTIDOPOMINAE 



Pseudolamellai3 absent. 

 Peristome single. 



Shell elongate-conic. 



Spiral sculpture absent Parachondrisca 



Spiral sculpture not absent Crossepoma 



Shell ovate Hispanipoma 



Peristome double. 



Intercostal spaces inconspicuously spirally striate Orcuttipoma 



Intercostal spaces not inconspicuously spirally striate, 

 but with spiral threads. 



Shell elongate-conic Parachondrops 



Shell elongate-ovate. 



Axial ribs vertebrated Colonina 



Axial ribs not vertebrated Haitipoma 



Pseudolamella present. 

 Peristome simple. 



Shell ovoid Kisslingia 



Shell elongate-conic Klattea 



Peristome double. 



Axial and spiral sculpture covering entire surface Licina 



Axial and spiral sculpture not covering entire surface. 



Outer peristome very broadly expanded Sallepoma 



Outer peristome not very broadly expanded Clydonopoma 



Genus PARACHONDRISCA Henderson and Bartsch 



1920. Parachondrisca Henderson and Bartsch, Proc. U. S. Nat. Mus., vol. 58, 

 pp. 65, 66. 



Shell elongate-conic, marked by axial riblets only, which are fused into 

 tufts at the summit. No trace of spiral sculpture, even on the umbilical 

 wall, is present. Operculum with rather distantly spaced, retractively 

 curved, strongly elevated, thin lamellae, which are fused on the inner 

 edge of the turns. They are most elevated at the inner edge of the 

 whorls and decrease outwardly, terminating before reaching the outer 

 margin of the chondroid basal plate. 



Type species : Cyclostoma umbricola Weinland = Parachondrisca nm- 

 hricola (Weinland). 



^' The term pseudolamella is here applied to the flat plate formed by the expansion and fusion 

 of the retractively curved opercular riblets on their outer edge, which produce an appearance 

 simulating the decidedly reflected lamella of certain anniilarine mollusks. The latter, however, 

 have the lamella free and not joined to the basal chondroid plate by riblets. The pseudolamella 

 may cover the entire ribbed surface of the opercular whorls or be restricted to the inner 

 margin, in which case the distal portion shows the ribbing only. Pseudolamellid Rhytidopomini- 

 nae seem restricted to Hispaniola. 



