20 STBOBILOPS, CANiVDA ANT) UNITED STATES. 



1. Strobilops labyrinthica (Say). PL 1, figs. 1-11. 



The shell is narrowly umbilieate, the -width of umbilicus 

 contained about 11 (9 to 12) times in the diameter of the 

 shell; very convexly conic or dome-shaped, the periphery ob- 

 tusely subangular. Whorls 5i/4, convex, very slowly widen- 

 ing, the first iy2 smooth, pale, the rest chestnut-brown, sculp- 

 tured with narrow obliquely radial ribs narrower than their 

 intervals, passing over the periphery but weakening at the 

 base, the first half of which is typically nearly smooth. The 

 aperture is semi-lunar. Peristome brown, expanded, thick. 

 The parietal lamella emerges to the edge of the parietal callus 

 and penetrates inward a little more than half a whorl. The 

 infraparietal lamella is much smaller, only shortly emerging, 

 the end visible in a basal view; inside it penetrates as far as 

 the parietal lamella. There is a low and slender interparietal 

 lamella between these lamellsB deep within; all three are 

 strongly nodose at the edge, the nodes armed with minute 

 prickles directed towards the aperture (PL 1, fig. 11). "Within 

 the basal and outer waUs, at the last third of the base, there 

 is a low, rather blunt columellar lamella and a forwardly 

 curving series of five (or six) unequal basopalatal folds; first 

 and second folds are large and high, the second longer; two 

 or three following folds are low and thin, the one immediately 

 above the periphery usually longer, and there is sometimes 

 another fold above it (PL 1, fig. 6, a topotype; also figs. 7, 9). 



Height 1.7, diam. 2.3 mm. (Philadelphia). 



Height 1.8, diam. 2.3 mm. (Philadelphia). 



Maine and Quebec west to Manitoba, Minnesota, Kansas and 

 Arkansas, south to Georgia and Alabama. Type locality, 

 Philadelphia, Pa. 



Helix labyrinthica Say, Journ. Acad. N. S. Phila., I, 1817, 

 p. 124. — Strohila labyrinthica Say, Morse, Terrestrial Pul- 

 monifera Maine, Journ. Portland Soc. N. H., I, p. 26, figs. 61- 

 67, pi. 8, f. 68.— BiNNEY, Terr. MolL, V, 1878, p. 259, text- 

 figs. 149-152, pi. 17, f. 3; pi. 5, f. o (teeth).— Strebel, Beitrag 

 Mexikanischer Land- und Siisswasser-Conch., IV, 1880, p. 43, 

 pi. 4, f. 6a (Ohio).— F. J. Ford, Naut. Ill, p. 106 (Sedgmck 

 Co., Ks.). — Sampson, Naut. VII-, p. 33 (Missouri). — Prime, 



