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. 



55 a. Polygyra albolabris dentata Tryon. 



Mesodon dentata TRYON, Man. of Conch., Vol. III., p. 150. 



Differs from albolabris 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, pi. xxix, fig. 5. 



Helix exoleta BINNEY, Terr. Moll. U. S., Vol. II, p. 131, pi. x. 

 Helix zaleta BINNEY, Bost. Journ. Nat. Hist., Vol. I, p. 492, pi. 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; spire a 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.) 

 27.00; " 22.00; " 19.00 " (7973.) 

 28.00; " 23.00; " 20.00 " (8092.) 



Animal: Resembling albolabris in general form. Coloi 

 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: ^ + f + * + i + f +|+^(6o-i -60); 



