20 THE NAUTILUS. 



NOTE ON LYMNAEA DESIDIOSA SAY. 



BY FRANK COLLINS BAKER. 



An examination of Say's specimens of L. desidiosa in the Academy 

 of Natural Sciences of Philadelphia reveals the fact that all subse- 

 quent naturalists have misunderstood this species and have given the 

 name to a species belonging to a different group of Lymnaeas. The 

 true desidiosa is a member of the palustris group, as shown by Say's 

 specimens and by a close study of Say's descriptions. The two 

 specimens in the Philadelphia Academy may be described as follows : 



Shell oblong-ovate, rather solid, color pale horn ; surface dull, 

 lines of growth crowded, conspicuous, crossed by impressed spiral 

 lines ; whorls 5, convex ; the body whorl is quite convex ; spire 

 acutely conic, about as long as the aperture ; sutures well impressed; 

 apex of l whorls, brownish horn; aperture long ovate; outer lip 

 thin, with an internal rib or varix ; inner lip reflected over and 

 appressed to the parietal wall, leaving a small umbilical chink ; 

 columelar axis with a distinct plait. 



Length 15.00, breadth 7.50, aperture length 8.00, breadth 3.00 

 mill. 



Length 14.25, breadth 7.50, aperture length 7.75, breadth 3.50 

 mill. 



The specimens bear the following label in the original hand- 



writing : 



Lymnaea desidiosa Say, Journ. Acad., v. 2, p. 169. T. Say, 

 Penn. ? (No. 58731). 



The figure in Binney (fig. 68) is said to be from an authentic 

 specimen in the Philadelphia Academy, but no such specimen is 

 now in existence, nor are the specimens mentioned from Cayuga 

 Lake to be found. In the absence of any other authentic material 

 Say's specimens must be taken as typical of desidiosa. A close 

 analysis of Say's description would seem to indicate that he did not 

 have the shell before him which has so long borne the name of 

 desidiosa. He says " It is closely allied to elodes, but the whorls are 

 more convex, one less in number, and the two terminal ones are 

 proportionately smaller." 1 This statement is repeated in the Amer- 

 ican Conchology. This statement of its relation to elodes would 



'Journ. Acad. Nat. Sci., ii, p. 169. 



