THE NATURAL HISTORY SURVEY. - 181 
distant; color brownish-horn, transparent; periphery rounded; 
sutures well impressed; whorls four, rapidly enlarging, the last 
half of the last whorl very rapidly enlarging as it approaches 
the aperture; spire flat or a trifle convex; aperture large, trans- 
versely rounded, somewhat expanded; peristome simple, with 
thickened edge; umbilicus small, round, deep, showing several 
of the volutions, the umbilical region strongly concave; base 
of shell convex (See Fig. 36). 
Greater diam.,4.25; lesser, 3.75; ht.,2.50; umbilicus diam., 0.50 mill. (10103.) 
irramete es ANNO BibOe MOE. a “ 0.50 “ (10104,) 
eee eT: S800" 20d tae ©” 0.50 <*> (0652) 
Pte SAAD;  A00r, Mh 2 SUR es i, OUR 2 S(T 2gGS 
Anmal: With a long, narrow, transparent foot, with pedal 
grooves as in arvboreus, head, neck and upper part of animal 
black or blackish, lighter on the side of the foot; the other 
characters as in ardoreus. Heart situated as in the previous 
species; pulsations regular and rapid, gs§ per minute when con- 
tracted and 130 when extended. Length of foot 6.00, width 
1.00 mill. (Shell 4.25 mill. greater diameter.) 
Jaw: Strongly arched, wide, roundly pointed at the ends, 
Fic. 37, 
Jaw of VITREA HAMMONIS Strém. (After Morse.) 
which are a little upturned; concave margin with a good sized, 
rounded median projection, and two or three smaller projec- 
tions on either side (Fig. 37). 
Radula formula: 2%4+3+4+3+22 (27—1-—27); teeth of 
the same general type as those of Zonitoides arboreus ; central 
narrow, tricuspid; laterals of same type, but bifid; marginals 
aculeate. There are about 55 rows of teeth. 
Distribution: North America, Europe, Asia. In North 
America from British America and Northern United States 
south to South Carolina and Colorado. 
Geological distribution: Pleistocene; Loess. 
Habitat: Same as Zonitoides arboreus and usually asso- 
ciated with that species. 
Remarks: This species is very closely related to Zonitoides 
arboreus but may be distinguished by its darker color, the more 
rapid enlargement of the last whorl and its different shape 
