154 THE CHICAGO ACADEMY OF SCIENCES. 
in and the tentacles are laid back and half contracted. The 
writer timed a large specimen of this species and found that it 
progressed 24 inches in 14 minutes. 
55a. Polygyra albolabris dentata Tryon. 
Mesodon dentata Tryon, Man. of Conch., Vol. III., p. 150. 
Differs from a/bolabris in possessing a tooth on the parie- 
tal wall. The variety is rare, but is found associated with the 
type in all localities. 
56. Polygyra exoleta Binney, pl. xxix, fig. 5. 
Flelix exoleta BINNEY, Terr. Moll. U.S., Vol. II, p. 181, pl. x. 
Flelix zaleta BINNEY, Bost. Journ. Nat. Hist., Vol. I; p. 492, pl. xx. 
Shell: Globose, solid, imperforate: surface shining, 
marked by numerous fine, oblique growth lines, which are 
faintly marked on the apical whorl; the growth lines are 
crossed by very fine spiral lines as in albolabris; color yellow- 
ish, sometimes dark horn; periphery rounded; sutures well im- 
pressed; whorls five to six, globose, the last ventricose, rather 
closely coiled; spirea little elevated, convex; aperture roundly 
lunate, contracted by the body-whorl, the base of the aperture 
forming an angle with the base of that portion of the body- 
whorl contracting the aperture; peristome broadly reflected 
white, sometimes a trifle grooved, with a small callosity near 
the base, terminations separated and connected by a thin cal- 
lus; parietal wall armed with a long, narrow tooth or denticle 
about midway between the terminations of the peristome; 
umbilicus covered (in the adult shell) by the white reflection of 
the peristome; base of shell rounded. 
Greater diameter, 24.00; lesser, 21.50; height, 16.50 mill. (7973.) 
x ‘i 27.00; “ 22.00; Fe ce (7973.) 
2“ a 28.00; ‘“ 23.00; 6 SEO ae (8092.) 
Animal: Resembling a/bolabris in general form. Color 
dirty white or yellowish-white, darker above; eye-peduncles 
jet black, a light zone surrounding the eyes; tentacles yellow- 
ish-white at base and black at tip; mantle yellowish-white; the 
animal may also be brownish or blackish. 
Heart situated near the upper junction of peristome with 
body-whorl: pulsations quite regular, seventy-five to seventy- 
seven per minute. 
Jaw: Of usual form, rather narrow, arcuate, attenuated 
at the ends; thirteen ribs,present. 
Radula formula: $#8,+$+$+4+4+8+5(60—1-—60); 
eee 
