THE NATURAL HISTORY SURVEY. Bol 
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 “vzcarinata is more cylindrical and en- 
larged at the termination, where it somewhat resembles the 
snout of the hog, while that of the dzcarvinata is more conical 
and without so sudden an enlargement at the end. The color 
of the dzcarinata is lighter. In the black markings they also 
differ. In the ¢#zcarvinata there is a single blotch anterior to 
the area between the eyes. In the dzcarinata this extends also 
behind this area; and in addition may be observed two quite 
black marks above the mouth, which the “#carinata does not 
seem to have. The tentacula of the dccarinatfa 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 “#carinata. 
Distribution: Apparently the same as ¢ricarinata. 
Geological distiibution: Pleistocene; Loess. 
Habitat: Same as tricarinata. 
Remarks: In a recent letter Mr. Bryant Walker an- 
nounced that in his opinion dzcavinata should be considered a 
distinct species from “#icarinata, since the shells of the two 
forms are always distinguishable. Uponreceipt 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 “#icarinata the upper surface slopes upwards from 
the carina to the suture, while in dzcarinata it slopes downwards, 
giving the upper surface a concave appearance. . 
Bicarinata is found in the Desplaines River and in Lake 
