150 THE CHICAGO ACADEMY OF SCIENCES. 



all have been subjected to some peculiarly unfavorable influence. The 

 specimens from Black Lake are a pure translucent white. If the forms 

 figured on the plate referred to (pi. XXII, figs. 1, 2) were constant 

 they would constitute a marked variety of stagnalis. Mr. Walker says 

 of these, in a recent letter, that they vary toward the normal form and 

 that in his opinion they are not entitled to be given varietal rank. 

 He also says: "The set I have varies greatly in shape and several 

 of them are deformed. Another has the edge of the lip completely 

 revolute. Figs. 2 and 3 are the most regular." In the Smithsonian 

 Institution there are three specimens similar to those figured by Mr. 

 Walker. These measure as follows : 



Aperture 



Length. Breadth. length. Breadth. 



33.00 16.50 22.00 10.25 mill. Lake Erie 



22.00 14.25 19.25 8.00 " Ruby Valley. 



29.00 15.00 18.50 9.00 



The Lake Erie specimen (No. 41716) was collected by Dr. Dall 

 and the Ruby Valley specimens (No. 27953) by Capt. Simpson. This 

 form is similar to var. acuminata Lam., clammys Bens., and succinea 

 Desh., which are peculiar to India. 



In the Niagara River at Squaw Island, near Buffalo, N. Y., occurs 

 a form of appressa with a much expanded aperture, recalling some 

 of the mutations named by European conchologists. Some specimens 

 have the upper part of the aperture much flattened. It is upon just 

 such material as this that some of the French conchologists have made 

 two score or more species and varieties of Lymnaa stagnalis. The 

 shell of stagnalis is frequently distorted, the whorls becoming scalari- 

 form and developing a marked shoulder. Such specimens have been 

 seen from Spoonbill Slough, Deuel County, South Dakota. 



Lymnaea stagnalis var. Plate XXII, figure 4. 



Limnoza stagnalis va-r. bottnica f WALKER, Nautilus, IX, p. 3, 1895. 



"Among the fresh-water pulmonates many interesting forms oc- 

 curred. The most noteworthy of them was a single example of a 

 deep-water form of Limnsea stagnalis L., dredged from ten meters 

 depth in Lake Michigan, at High Island Harbor, in the Beaver Island. 

 It is about 23 mm. in length, exceedingly fragile, of a pure translucent 

 white, and, though somewhat larger and differently proportioned, ap- 

 pears to be analagous to the var. bottnica of Clessin from Sweden." 

 (Walker, Nautilus, p. 3.) 



This is a peculiar shell and additional material may prove it to 

 represent a recognizable race of stagnalis. Mr. Walker says of it: 

 "The white form of L. stagnalis mentioned in Nautilus IX, p. 3, was 



