2 14 Mr. J. E. Gray on the Clausium of Clausilia. 



from P/'/ja, which the author of the paper is willing to con- 

 der a distinct genus of the same rank as his VylindreUa, 



There are several other species referable to this group, 

 besides those named by Dr. Pfeiffcr; among others, a veiy 

 large and beautiful one, the giant of the genus, named Pupa 

 purpurea bj the English authors, which has a very slender 

 tapering tip about an inch long, and then the whorl suddenly 

 enlarges and forms a broad ovate shell; the top which held 

 the body of the animal in its young state being far too small 

 for its rapidly increased size, falls off and leaves a blunt end. 



A second species nearly as large is Helix M auger a> of Wood, 

 Cat. Sup. t. 7- f. 31. = Helix ignifera, Ferussac, n. 494. 



If the shell which I possess under the name of Clausilia 

 torticollis is correctly named, it is a true Clausilia. 



I cannot agree with Dr. L. PfeirTer in regarding the clau- 

 sium of Clausilia as u evidently analogous to the operculum 

 of several molluscous genera." First, It is not attached 

 to the animal as the operculum always is, but is a mere ap- 

 pendage to the mouth of the shell. Secondly, It is only 

 formed when the animal has nearly reached its full growth, 

 when it is about to complete the mouth of its shell, and not 

 developed in the embryo of the animal while yet in the egg, 

 as is the case with the operculum. Thirdly, The genus be- 

 longs to a group of molluscous animals which are never 

 operculated. 



From the above considerations I have always regarded the 

 clausium as a peculiar modification of a tooth or plait ; I 

 think, that when its position, use, and mode of formation is 

 considered, this will be found to be the case. If this be 

 correct, I do not then see how the genus Clausilia is to be 

 separated according to Dr. L. PfeifTer's views from Bulimus ; 

 and as Cylindrella Chemnitziana has the ovate mouth, and 

 the sinistral whorls of Clausilia, and I believe a rudimentary 

 clausium, it will be necessary, if his views are carried out, to 

 unite his genus Cylindrella to the same great group. 



Yours very truly, 



John Edward Gray. 



British Museum, May 14, 1840. 



