THE NAUTILUS. 
115 
but the apex is slightly sunken ; whorls nearly three, slightly con¬ 
vex, rapidly widening, acutely keeled at the periphery, the keel 
projecting above the suture on the penultimate whorl in most adult 
specimens. On the last whorl the keel is about median in position, 
is acute, as if pinched out, and extends to the aperture. Base of 
shell convex, rising toward the umbilicus, which is moderately large 
and funnel-shaped, with very obtusely angled margin. Aperture 
small, oblique, sub-rhombic ; the lip strongly thickened within. Alt. 
J *8, diam. 3’4 mm.; width of aperture T6 ram. 
Woodville, Alabama (Prof. PI. E. Sargent). This is a smaller 
species than P. exacutus, with much smaller less oblique aperture, 
thick lip, and not so flattened. It differs from P. dilatatus in the 
acute peripheral keel, etc. 
Amnicola olivacea n. sp. 
Shell olive colored, somewhat intermediate in form between an 
ordinary Amnicola and Pomatiopsis lapidaria. Spire elevated, the 
apex rather acute. Whorls 5, very convex. Aperture ovate, less 
than half the length of the shell, angular above; peristome free ex¬ 
cept for a very short distance on the parietal wall; umbilicus 
rather large. Surface smooth ; coated with iron oxide in the adult 
specimens seen. 
Alt. 4’2, diam. 2'5 mm. (Male?). 
Alt. 4‘2, diam. 3 mm. (Female?). 
Huntsville, Ala. (coll, by Prof. H. E. Sargent; see Nautilus for 
December, 1894, p. 95). 
This form is quite distinct from other Amnicola, being of more 
elongated contour than any other Northern forms except A. lustri- 
ca. Its nearest allies are some of the smaller slender Floridian forms, 
but none of these have such convex whorls. As I have seen dry 
specimens only, I have not verified the reference of the stouter in¬ 
dividuals to the female sex, but from analogy with other species this 
is probable. The supposed males have much the general appear¬ 
ance of Pomatiopsis eincinnatiensis. 
Planorbis bicarinatus aroostookensis n. var. 
Shell having the spire and umbilicus very deep, the latter funnel* 
shaped as in typical bicarinatus, but both upper and lower keels en¬ 
tirely obsolete or rounded off on last whorl, which has the aspect of 
that of P. trivolvis. Surface minutely striated spirally as in P. bi- 
cdrinatus. Aperture less angular and less produced below than in 
bicarinatus, in consequence of the rounding of the whorls. Diam. 
