124 BULLETIN 181, UlSnTEiD STATES NIATTONAL MUSOEUM 



Suture well impressed, less so on the last half of the last turn, which 

 is appressed to the summit. Periphery strongly rounded, marked by 

 the feeble continuation of the axial riblets. Base inflated, strongly 

 rounded, narrowly umbilicated with a weak cord marking the outer 

 edge of the umbilicus. The base outside of the umbilicus shows a 

 few weak pits outside of the basal cord and mere indications of obso- 

 lete nodulations, which fade out toward the end of the last turn. 

 The umbilical wall is marked by moderately strong incremental lines. 

 Aperture circular, protracted into a slight angle at the posterior 

 angle; peristome somewhat thickened all around. Operculum 

 typically cyclobakerid. 



The type, U.S.N.M. No. 535981, was collected by Orcutt near Bath, 

 St. Thomas Parish, Jamaica. It has lost part of the early turns; 

 the 3 remaining measure: Height, 12.4 mm.; gi-eater diameter, 16.6 

 mm.; lesser diameter, 13.2 mm. 



The species seems to extend through the Morant Bay region, St. 

 Thomas Parish. 



Genus APEROSTOMA Troschel 



1847. Aperostoma Troschel, Zeitschr. Malak., vol. 4, p. 44. 



1847. Aperostoma Pteiffeb, ilid., p. 47. (Type designation, Cyclostoma (Apero- 

 stoma) Manchetianum Moricand. ) 



1850. Aperostoma Pktit, Journ. Conchyl., vol. 1, p. 38 (C. giganteum Sowerby 

 designated as type). 



1852. Aperostoma Herrmannsen, Indicis generum malacozoornm primordia, vol. 

 2, Suppl., p. 10 (C. mexicanum Menke designated as type). 



Troschel (loc. cit.) in 1847 divided the cyclostomids into eight 

 genera. On page 44 he created the genus Aperostoma and named 

 three species under it, namely, Cydostonia ^volvulus Lamarck, C. 

 mexicanum Menke, and C. hlanchetianum Moricand, without designat- 

 ing a type. Pfeiffer, in the article following Troschel's, discussed 

 his own work on the group and commended Troschel's endeavors, 

 which he accepted as sound, but he said that genus 4, Aperostomxi^ 

 contains heterogeneous elements, namely, some with calcareous oper- 

 culum and some with horny. He restricted the name Aperostom,a to 

 shells with a calcareous operculum. He placed those with a horny 

 operculum in Cyclophorus Montford, citing as type G. volvulus 

 MiUler. 



This restriction of Aperostoma Troschel removes C. volvvhis 

 Lamarck and C. mexwanumy Menke from the genus and leaves only 

 C hlanchetianum Moricand, which becomes its type. 



KEY TO THE SUBGENERA OF WEST INDIAN APEROSTOMA 



Umbilicus bounded by a keel Cycladamsia 



Umbilicus not bounded by a keel. 



Sculpture rugose Austrocyclotus 



Sculpture not rugose Cyclohidalgoa 



