THE CTOLOPHORII) LAND MOLLUSKS OF AMERICA 255 



postnuclear whorls are moderately well rounded, the last one having 

 a depressed area a little anterior to the summit. The summit itself, 

 at least on the last whorl, shows like a cord. The postnuclear whorls 

 are marked by retractively slanting axial riblets, which on the penul- 

 timate whorl are about as wide as the spaces that separate them; on 

 the last half of the last whorl they gradually become weakened and 

 finally evanescent. Suture very conspicously impressed. Periphery 

 of the last whorl feebly angulated. Base narrowly umbilicated, 

 inflated, strongly rounded, and marked by the continuation of the 

 axial ribs which become irregular and rather poorly emphasized on 

 the umbilical wall. Aperture large with a moderately conspicuous 

 angulation at the posterior angle ; peristome simple ; outer lip rather 

 produced, thin; the inner slightly thickened. The parietal wall is 

 covered by a thick callus, which is separated from the preceding turn 

 by an impressed line, rendering the peritreme complete. 



The type, U.S.N.M. No. 57285, was collected by Louis Agassiz in 

 Brazil, probably in the Amazon River region, since the Agassiz 

 expedition covered that field. It had 4.4 whorls and measures: 

 Height, 15.7 mm.; greater diameter, 28.3 mm.; lesser diameter, 19 

 mm. Height of aperture, 11.1 mm.; diameter, 13.7 mm. 



This species is readily distinguished from A. (A.) nevadeTise by 

 its deeply impressed suture. 



APEROSTOMA (APEROSTOMA) NEVADENSE, new species 



Plate 37, Figtjees 15-17 



Shell helicoid, the upper surface covered by a brownish olivaceous 

 periostracum, which on the last half of the last turn becomes olive. 

 There is a narrow, faint, spiral, lighter zone immediately above the 

 periphery. The base has a pale olivaceous-brown band covering one- 

 fifth of the base, anterior to the periphery. The rest is olivaceous 

 horn colored. The nucleus consists of 2, rather large, well-rounded, 

 smooth turns. The post-nuclear whorls are well rounded, the last one 

 is slightly flattened toward the sutufe. The postnuclear whorls are 

 marked by very poorly developed, irregular, somewhat wavy axial 

 riblets. Suture weakly impressed. On the last half of the last turn 

 the riblets become decidedly irregular and almost obsolete. Periphery 

 obsoletely angulated. Base narrowly umbilicated, inflated, well 

 rounded, and marked by irregularly developed and spaced riblets, 

 which give it a rough surface, even rougher than the spire. Aperture 

 broadly oval, weakly angulated at the posterier angle; peristome 

 simple; the outer lip thin; the inner slightly thickened and slightly 

 reflected. The parietal wall is covered by a moderately thick callus, 

 which renders the peritfeme complete. 



