THE NATURAL HISTORY SURVEY. 351 



hind by several irregular white spots, the anterior ones being 

 the larger. Branchia translucent, superior portion blackish, 

 bordered with white spots and occasionally obtruded; eyes 

 round and deep black, placed at the posterior base of the ten- 

 tacula, surrounded by a white area; tentacula long, rather 

 tapering, obtuse at the end; filament rather short, translucent 

 with longitudinal white lines; foot wide and furcate anteriorly, 

 where minute white spots may be observed. Operculum thin, 

 semitransparent, light horn color, increment circular and 

 rather coarse." 



"The head of the tricarinata is more cylindrical and en- 

 larged at the termination, where it somewhat resembles the 

 snout of the hog, while that of the bicarinata is more conical 

 and without so sudden an enlargement at the end. The color 

 of the bicarinata is lighter. In the black markings they also 

 differ. In the tricarinata there is a single blotch anterior to 

 the area between the eyes. In the bicarinata this extends also 

 behind this area; and in addition may be observed two quite 

 black marks above the mouth, which the tricarinata does not 

 seem to have. The tentacula of the bicarinata are larger and 

 more filiform. When in motion, the anterior portions of the 

 lobes of the foot are pointed, and recurved or hooked." 



Radula: Apparently not differing from tricarinata. 



Distribution: Apparently the same as tricarinata. 



Geological distribution : Pleistocene; Loess. 



Habitat: Same as tricarinata. 



Remarks: In a recent letter Mr. Bryant Walker an- 

 nounced that in his opinion bicarinata should be considered a 

 distinct species from tricarinata, since the shells of the two 

 forms are always distinguishable. Upon receipt of Mr. Walk- 

 er's letter, the writerexamined all of the material in the Acad- 

 emy's collection, besides carefully reading the descriptions 

 of Say and Lea. The two species are undoubtedly distinct, 

 tricarinata being elevated, the width equaling the height, while 

 bicarinata is depressed and the height is four-fifths of the 

 width. The former is normally tricarinate while the latter is 

 bicarinate, although both bi- and tri-carinate forms occur in both 

 species. In tricarinata the upper surface slopes upwards from 

 the carina to the suture, while in bicarinata it slopes downwards, 

 giving the upper surface a concave appearance. 



Bicarinata is found in the Desplaines River and in Lake 



