156 THE CHICAGO ACADEMY OF SCIENCES. 



Remarks: The present species very closely resembles 

 albolabris, but differs in its smaller, more globose shell, the 

 almost universal presence of the tooth on the parietal wall and 

 the less contracted and rounded aperture. The two species 

 are almost always found associated together. The shell is car- 

 ried sightly tilted over the back during locomotion. This spe- 

 cies is found only in the southern and western regions. 



57. Polygyra thyroides Say, pi. xxix, figs. 2, 7. 



Helix thyroides SAY, Nich. Encycl., Am. ed., 1817, 1818, 1819; Jour. 



Phil. Acad., Vol. I, p. 123, 1817. 

 Helix bucculenta GOULD, Proc. Bost. Soc. Nat. Hist., Vol. Ill, p. 40, 1848. 



(Variety.) 

 Polygyra thyroides pitlchella CK.LL. The Nautilus, Vol. XI, p. 95, 1898. 



(Variety.) 

 Polygyra thyroides sanctisiinonis Pilsbry, The Nautilus, Vol. XV. p. 8, 



1901. (Variety.) 



Shell: Depressed, thin, umbilicated; surface covered with 

 numerous crowded, oblique lines of growth which are crossed 

 by very fine spiral lines; the nuclear whorl is almost smooth; 

 color light yellowish, brownish, horn color or russet, sometimes 

 inclined to pinkish; peripheryrounded; sutures well impressed; 

 whorls five, depressed-globose, rapidly increasing in size; spire 

 somewhat elevated; aperture lunate, spreading, contracted by 

 the peristome: peristome widely reflected, thin, grooved, white, 

 terminations connected by a thin callus; parietal wall with a 

 more or less well developed, white tooth, which is longer than 

 wide, placed obliquely to the plane of the aperture; columella 

 flexuous; umbilicus open, partly covered by the reflected peri- 

 stome; base of shell rounded. 



Greater diameter, 28.00; lesser, 23.00; height, 18.00 mill. (9920.) 

 28.00; " 22.00; " 16.00 " (8404.) 

 26.00; " 21.25; " 17.00 " (10668.) 

 24.50; " 21.00; " 16.50 " (7733.) 

 21.50; " 18.00; " 15.00 " (8374.) 



Animal: Grayish or yellowish-white, darker on the head 

 and eye-peduncles, dirty white on base of foot; eye-peduncles 

 long, tapering, thin, eyes black; foot long and narrow, the 

 length of a good-sized individual being 43 and the width 5 mm.; 

 the posterior extremity of the foot terminates in an acute an- 

 gle; the heart is situated near the junction of the upper part of 

 the peristome with the body-whorl; the pulsations are irregular 

 and number from seventy to seventy-three when the animal 

 is drawn into its shell, but become regular and number eighty- 



