210 BULLETIN 181, UNITEiD STATES NlATIOOSTiAL MUSEUM 



strongly arched, forming a decidedly sigmoid line with the callus of 

 the parietal wall. The parietal callus is thick and separated from 

 the preceding whorl by a stronger impressed line. Operculum typi- 

 cally neocyclotid. 



The type, U.S.N.M. No. 523674, was collected by F. E. Sumichrast in 

 Chontales Forest, Nicaragua. It has 3.2 whorls remaining and meas- 

 ures; Height, 17.4 mm. ; greater diameter, 23.5 mm. ; lesser diameter, 

 16.3 mm. Height of aperture, 12 mm. ; diameter, 13.1 mm. 



U.S.N.M. No. 24023 contains 2 topotypes. 



In size and sculpture this subspecies recalls A. (N.) dysoni afrne 

 (v. Martens) , from which it can be distinguished by its more thickened 

 inner lip, which is also more incised on the parietal wall. The pos- 

 terior angle of the aperture is also much more strongly angulated and 

 the aperture is not quite so wide. 



APEROSTOMA (NEOCYCLOTUS) DYSONI AFFINE (von Martens) 



Plate 28, Figxjbes 22-24 



1890. Cyclotus (Aperostoma) dysoni afflnis von Martens, Biologia CentraU- 



Americana, p. 4, pi. 1, fig. 1. 

 1897. Neocyclotus (Neocyclotus) dysoni afflnis Kobelt and Mollendorff, 



Nachrbl. deutschen malak. Ges., vol. 29, p. 137. 

 1923. Poteria (Neocyclotus) dysoni afflnis H. B. Baker, Occ. Pap. Mus. Zool. 



Univ. Michigan, No. 137, p. 34. 



Shell rather large, helicoid, rather thin, covered with an olivaceous 

 straw-colored periostracum ; the anterior half of the base is a little 

 paler than the rest. The denuded early whorls are of livid color; 

 the later turns, when denuded, are soiled white. The nucleus con- 

 sists of 2 small, well-rounded, smooth turns. The postnuclear whorls 

 are strongly rounded, except the last, which has an impressed groove 

 a little below the summit while at the summit it is appressed to the pre- 

 ceding turn. The postnuclear whorls are marked by vermiculated, 

 retractively slanting axial riblets, which are a little more distantly 

 spaced than the spaces that separate them. Suture well impressed. 

 Periphery well rounded. Base narrowly umbilicated, marked on 

 the posterior half by the sculpture corresponding to that of the 

 upper surface of the last turn. The anterior half and umbilical 

 wall are marked by rather coarse, rather riblike incremental elements. 

 Aperture subcircular ; peristome simple, rather effuse on the outer lip, 

 not greatly thickened on the inner lip. The parietal wall is covered 

 by a moderately thick callus. The junctions of the parietal wall and 

 the outer lip form a slight angle at the posterior angle of the aperture. 

 Operculum typically neocyclotid. 



The specimen described and figured is one of five, U.S.N.M. No. 

 228661, collected by August Busck in Panama. It has 4.4 whorls and 



