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AN ARRANGEMENT OF THE AMERICAN CYCLOSTOMATID^, 

 WITH A REVISION OF THE NOMENCLATURE. 



By Prof. William H. Dall, D.Sc. 



Bead 9th December, 1904. 



The following arrangement shows in outline the results of a somewhat 

 extended investigation into the nomenclatorial history and diagnostic 

 characters of the American members of this family. 



Genus ANNULARIA, Schumacher, 1817. 



Rhachidian tooth of the radula, narrow, uni cuspidate. 

 Type : Turbo lincina, Linn. 



This is Annularia, Schumacher, after the deduction of Cyclophorus, 

 which dates from 1810. 



Subgenus Annulaeia, s.s. 



Operculum horny, multispiral, circular, with a depressed central 

 nucleus, and an elevated, calcareous, continuous, spirally gyrate 

 lamina externally, which is obliquely striate, with the coils separated 

 by a narrow channel at the suture, and with the opercular periphery 

 sulcate. 



Section Jamaicia, C. B. Adams, 1850. 



Type : J. anomala^ Adams. Jamaica. 



Operculum externally very convex, internally concave ; few- 

 whorled, with subcentral nucleus, and gyrate calcareous lamina. 



Section Diplopoma, Pfeiffer, 1859. 



Type : D. architectonicum (Gundlach). Cuba. 



Operculum paucispiral, with a lamina as in Annularia, s.s., but 

 with the peripheral sulcus exceptionally deep. 



Section Adamsiella, Pfeiffer, 1851. 



Type: A. mirab His {Wood). Jamaica. 



Operculum circular, thin, paucispiral, with a central nucleus, and 

 very delicate, gyrate, calcareous lamina, of which the coils are separated 

 by deep channels ; the shell pupiform, small. 



Genus BHYTIDOPOMA, Sykes, 1901. 



Type : Ctenopoma rugulosum, Pfeiffer. 



Operculum flat, circular, with subcentral nucleus, and rather 

 rapidly enlarging whorls ; calcareous layer rising in low, regularly 

 spaced lamellae, in harmony with the incremental lines j calcareous 



