LYMN^EHXE OF NORTH AMERICA. 319 



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 1 (italics the author's) : "It is closely allied to 

 elodes, but the whorls are more convex, one less in number, and the 

 two terminal ones are proportionately smaller." This statement is 

 repeated in the American Conchology. This comparison with elodes 

 would scarcely have been made by Say, who possessed a peculiarly 

 discriminating sense of minute differences between shells, if he had 

 been describing the shell historically known as desidiosa. The size of 

 the Philadelphia specimens (15 mill.) also corresponds pretty well with 

 the size given by Say (7/10 of an inch = about 17 mill.). The most 

 convincing fact to the writer is the presence of a specimen of "desidi- 

 osa" (authors) in the Philadelphia Academy marked "Lymnaea , 



Canandaigua Lake. T. Say" (No. 58732), showing that the form 

 usually called desidiosa is not the one so called by Say. Prof. Edward 

 S. Morse, who made the drawings for Binney's work, has been unable 

 to add to our knowledge concerning the specimen figured by Binney. 

 During the summer of 1907 the writer made three trips to Cayuga 

 Lake, one to the south end at Ithaca, and two to the north end at the 

 town of Cayuga, with the hope of securing specimens which would 

 correspond with Say's specimens. Three whole days were spent in 

 exploring several miles of the shore and the small creeks, and while 

 specimens of both palustris and obrussa were obtained, not a single 

 specimen was found which agreed with Say's desidiosa. The palustris 

 were the large, thin-shelled form and the obrussa were rather small 

 specimens, not at all like the description or specimens of desidiosa. 

 As Say gave no particular part of Cayuga Lake as the identical spot 

 in which the types were collected, it renders the task of finding loco- 

 types well nigh impossible, since the lake is thirty-eight miles in length. 

 Recently, Miss Mary Walker, of Buffalo, New York, sent the 

 writer a number of shells from Young's Quarry, Williamsville, New 

 York, which are identical with Say's specimens of desidiosa, having 

 the same number of whorls and almost the same measurements. These 

 are given for comparison. 



Length. Breadth. Aperture length. Breadth. 

 15.00 7.50 8.00 3.00 mill. Say's specimens 



14.25 7.50 7.75 3.50 " 



15.00 8.00 8.00 4.00 " Miss Walker's 



14.00 8.00 8.00 3.50 " " " 



Say's figure in the American Conchology (plate 55, fig. 3) corre- 

 sponds with the specimens from Williamsville, all having the peculiar 



Mourn. Acad. Nat. Sci., II, p. 169. 



