THE NATURAL HISTORY SURVEY. 301 
_the lower carination; three on the peripheral wall, the two 
upper ones being prominent, short, thick and triangular, and the 
lower one more or less lamelliform and situated on the base 
of the aperture, and one small conic tooth near the superior 
junction of the peristome with the body-wall; peristome thin, 
acute, slightly thickened inside, the superior margin a trifle 
produced; interior of aperture pearly-white, with a band of 
reddish just within the aperture extending parallel to the edge 
of.the aperture. In some specimens there is a sixth tooth, 
small, acute, elevated, just below the large one on the parietal 
wall; this, however, is not always developed (Fig. Ior). 
Length, 2.50; width, 6.00; aperture length, 2.50; width, 1.25 mill. (8473.) 
“ 900; “ 5.00; « «“ 900; * 1.00 “ (8478. 
« 975: « 6.00; « “« 995; 150 « — (8474.) 
i B00: 3. BOD « 950; “© 2.00 “ (12368.) 
Animai: With a rounded foot which is rather wide; head 
distinct, somewhat auriculate; tentacles very long and fili- 
Ere, Lot 
Aperture of SEGMENTINA ARMIGERA Say, showing number and posi- 
tion of teeth. (Original.) 
form, one and one-half-times as long as the foot; eyes placed 
as in Planorbis ; color blackish, lighter on edge of foot and ten- 
tacles; respiratory groove long and pointed, thin and transpar- 
ent. The foot measures 2% by % mill. 
Faw: Not differing from that of Planordis. 
Radula formula: #,.+3+4+3+2, (18—1-—18); central 
tooth with a long, narrow base of attachment, expanded on the 
lower, outer corners; reflection wide, bicuspid; lateral teeth 
wide, a trifle longer than wide, tricuspid, the center cusp long, 
wide and sharp, and the side cusps short and sharp; marginal 
teeth at first similar to laterals with the addition of a second 
small outer cusp; the marginals become wide and low toward 
the margin and three small outer cusps are developed (Fig. 
102). 
Genitaha: Not examined. 
