47 



NOTES ON SOME KNOWN SPECIES OF 



PLEGTOPYLIS, AND DESCRIPTION OF A NEW 



VARIETY OF PLEGTOPYLIS PLECTOSTOMA, BENS. 



By G. K. GUDE, F.Z.S. 



Since concluding my series of articles on the genus PledojvjUs in 

 " Science Gossip " I have received from various sources a number of 

 shells of this group. 



From Mr. E. Boubee of Paris I have received a specimen of P. 

 jovia, Mab., and one of P. scJUumhergeri, Morlet, and from Mr. W. F. 

 Webb, of Albion, N.Y., one specimen of P. viUedaryi, Ancey ; three 

 species, the armature of which I had not hitherto examined. These 

 materials enable me to supplement my remarks on these structures in 

 "Science Gossip," 1897, N.S., vol. iv, pp. 138, 139, and to add figures 

 of the plates, folds, and denticles in situ. 



A comparison of these three species has shown that they are very 

 closely allied, and that there is no difference of diagnostic value 

 between the armatures. They differ, however, in external aspect 

 sufficiently to rank as separate forms. P. Jovia is the largest of the 

 three, while P. viUedaryi is the smallest, P. schlumhergeri being 

 intermediate in size. The latter may also be distinguished by the 

 raised flexuous ridge on the parietal callus, being much less developed 

 than in the other two species, where this process assumes a tongue- 

 shaped form. 



a. b. 



Fig. I . — ritdopyUs jovia. 



a. Parietal armature. b. Palatal armature. 



In P. jovia the palatal folds numbers 2, 3, 4 and 5 are more vertical, 

 and their extremities more angularly deflected, than in P. scJihcmhenjeri, 

 while the parietal plate in the former is stronger and more curved 

 than in the latter. 



