119 



NOTE ON THE CLAUSILIUM OF A CHINESE SPECIES OF 

 CLA US ILIA. 



By Professor H. A. Pilsbry. 



Head IQth April, 1908. 



In the course of some studies on Chinese Clausiliae I had occasion 

 to examine the structure of C. Boclci described by our fellow-member 

 Mr. E. R. Sykes in these Proceedings} This species is reckoned by its 

 author to be a member of the section Pseudonenia. It agrees fully with 

 that group in characters of the shell and in the general shape of the 

 clausilium ; but there is, on the outer face of the latter, at its lower 

 third, a stout acute hook, arising near the palatal side, and directed 

 transversely to the length of the plate, as shown in Figs, a and h. 

 No such structure has been observed in any other Pseudonenia, or in 

 fact in any other Clausilia known to me. The only comparable 



Clausilium of Clausilia Bocki, Sykes. a, external view ; b, view from above ; 



c, inside. 



structure, so far as I know, is found in the section Parazwptyx, Pils.,' 

 in which there is a transverse plate or buttress across the outside of 

 the clausilium. Parazaptyx is a Loochooan form, not at all nearly 

 related to C. Boclci. It belongs to another line of specialization. 



In the case of Parazaptyx I had thought the function of the 

 transverse buttress might be to strengthen the clausilium ; but 

 obviously no such idea can be entertained regarding the hook of 

 C. Bocki. The hook on this clausilium reminds one of those inwardly 

 projecting hooks in the apertures of some Polygyras, which seem 

 adapted to catch and hold intending intruders rather than to exclude 

 them. 



» Proc. Malac. Soc, vol. i, p. 263 (1895). 



2 Proc. Acad. Nat. Sci. Pliilad., 1904, p. 834, pi. Ivii, figs. 101, 104. 



