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, pl. xxix, figs. 2, 7. 
Flelix thyrotdes Say, Nich. Encycl., Am. ed., 1817, 1818, 1819; Jour. 
Phil. Acad., Vol. I, p. 128, 1817. 
Helix bucculenta GOULD, Proc. Bost. Soc. Nat. Hist., Vol. III, p. 40, 1848. 
(Variety.) 
Polygyra thyroides pulchella CKLL. The Nautilus, Vol. XI, p. 95, 1898. 
(Variety.) ; 
Polygyra thyrotdes sanctistmonis 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; periphery rounded; 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.) 
e = 7c} |) pai || Ma 16.00 “ (8404.) 
.3 *y 2600; * A SL2a se is 17.00 “ (10668.) 
; a 24.805 (SS 2 OOe: a att 16.50 “  (7733.) 
rs as 21.505 0 AB DOSS set 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- 
