214 BULLETEN 181, UNITEiD STATES NlATTOINlAiL MUSEUM 



are somewhat inflated, well rounded. The penultimate whorl is 

 marked by somewhat wavy, retractively slanting axial ribs; the 

 waviness and vermiculations of these become intensified on the 

 last turn, the last part of which is very rough and irregular in 

 sculpture. The last whorl rounds evenly toward the summit, leav- 

 ing, however, a narrow, somewhat thickened, rounded cord near the 

 suture. Suture well impressed. Periphery well rounded. Base 

 narrowly openly umbilicated, inflated, well rounded and marked by 

 the continuation of the sculpture, which characterizes the upper 

 surface of the last whorl, except the umbilical wall, in which 

 the vermiculations are not present, and which is marked by moder- 

 ately rough riblike incremental elements. Aperture very broadly 

 pear-shaped, produced at the posterior angle; peristome simple, the 

 outer lip slightly thickened ; the inner a trifle more so. The parietal 

 wall is covered by a callus as thick as the columellar lip, and separated 

 from the preceding turn by a well-impressed groove. Operculum 

 typically neocyclotid. 



The type, U.S.N.M. No. 524003, was received from M. Valerio and 

 comes from an elevation of 1,480 meters at Cervantes, Costa Kica. 

 It has 4.7 whorls and measures: Height, 20 mm.; greater diameter, 

 26 mm.; lesser diameter, 18 mm. Height of aperture, 12.5 mm.; 

 diameter, 12.9 mm. 



U.S.N.M. No. 525005 contains three topotypes from the same source. 



This subspecies has the axial ribs of the penultimate whorl vermicu- 

 lated and the base bicolor, characters that differentiate it from A. (N.) 

 nicaraguense, in which the base is not bicolor. A. (N.) nicaraguense 

 also is smaller. 



APEROSTOMA (NEOCYCLOTUS) DYSONI NICARAGUENSE, new subspecies 

 Plate 29, Figthjes 16-18 



Shell of medium size, helicoid, covered by a pale olivaceous peri- 

 ostracum, with the early whorls pinkish. The nucleus consists of 2 

 small well-rounded whorls. The postnuclear whorls are strongly 

 rounded ; the penultimate one is marked by wavy axial riblets, which 

 are a little narrower than the spaces that separate them. The last 

 whorl is marked by feeble, more wavy, slightly vermiculated axial 

 riblets, which grow irregular on the last portion of this turn. There 

 is a slight impressed area a little below the summit, which is tumid. 

 Suture strongly impressed. Periphery well rounded. Base quite nar- 

 rowly umbilicated, inflated, strongly rounded, and marked by the con- 

 tinuation of the sculpture, which characterizes the upper surface of 

 the last turn and which extends to the umbilical wall. The umbilical 

 wall is marked by irregular low riblike incremental lines. Aperture 

 very broadly ovate, slightly angiilated at the posterior angle ; peristome 



