320 THE CHICAGO ACADEMY OF SCIENCES. 
obese body whorl. Say himself identifies desidiosa from western New 
York in Long’s Expedition, II, p. 263, where he says, “Lymneus de- 
sidiosus nob. Falls of Niagara.” Some of these specimens, as well as 
others from Seneca Lake, agree fairly well with Binney’s figure 68, 
and also with Say’s specimens. Binney’s figure 68 is also unlike the 
historical desidiosa, which rarely has such a uniformly oval aperture. 
There are, however, occasional specimens of obrussa which compare 
as favorably with Binney’s figure 68 as do the specimens mentioned 
above, and for this reason it seems best to refer it to obrussa with a 
query. (Compare figures 10 and 11, plate XX VI, with Binney’s figure 
68.) Another significant fact is that when Say described obrussa, in 
1825, he made no reference to desidiosa, which was described four 
years earlier (1821). This fact, together with his comparison with 
clodes, is to the author conclusive evidence of the distinction of these 
two species. 
The history of desidiosa in the American monographs is interesting 
_and clearly indicates that since Say’s time little attention has been given 
to closely analyzing this species. In all of his references, Say distinctly 
indicates a shell of the palustris type. Haldeman describes and figures 
the form here distinguished as obrussa and not the true desidiosa. 
(Compare his plate with Say’s fig. 8.) Many of Haldeman’s figures 
are abnormal and do not represent obrussa as it is usually developed. 
Tryon, in his continuation of Haldeman’s work (p. 104), states that 
many of the figures on this plate are not desidiosa, but a form of 
columella (macrostoma). In this statement Tryon is wrong and could 
scarcely have seen Haldeman’s specimens, for a recent examination 
proved them all to be referable to obrussa (desidiosa of authors), 
although, as stated above, several of the specimens are abnormal. The 
writer has collected many specimens similar to those figured on Halde- 
man’s plate. Binney, in his Land and Fresh-Water Shells of North 
America, part II, makes obrussa a synonym of desidiosa, thus showing 
that he considered the latter the small, smooth form and not the true 
desidiosa of Say, and his figure 68 is questionable for this reason. In 
Baker’s Mollusca of the Chicago Area, obrussa is described and figured 
as desidiosa. Recently, Dr. W. H. Dall, in his Alaska Mollusca (p. 73, 
fig. 51), figures Say’s obrussa under desidiosa, but also refers, in his 
synonymy, to Binney’s figure 68. The European monographs have 
given figures referable to obrussa rather than to desidiosa. 
Amidst the uncertainties caused by the absence of Say’s types we 
must look for a shell which is closely allied to elodes, but is smaller, 
with more convex whorls, and possesses 5 instead of 6 whorls. Such 
