224 BULLETIN 181, UlS^TEiD SWATES NlATTIOflSnAiL MUSETJM 



THE GROUP OF APEROSTOMA (APEROSTOMA) UMBILICATUM 



This group embraces the species having the upper surface of the 

 last whorl malleated. 



APEROSTOMA (APEROSTOMA) UMBILICATUM, new species 

 Plate 31, Figubes 1-3 



Shell very depressed-helicoid, very dark brown; the early whorls 

 paler; interior of aperture bluish white. The nucleus consists of 2 

 small, well-rounded, smooth turns; the postnuclear whorls are mod- 

 erately rounded and marked by retractively slanting lines of growth 

 and numerous, very rough malleations. Suture strongly impressed. 

 Periphery rendered decidedly angulated by a low keel. Base very 

 openly umbilicated, somewhat inflated, strongly rounded, and marked 

 by the continuation of the axial sculpture and strong malleations, 

 which on the posterior half also produce several impressed spiral 

 lines. The umbilical wall also is malleated. Aperture irregularly 

 broadly tear-shaped and drawn out into a rather broad angle at the 

 posterior angle. There is a groove in the center of this angulation ; 

 peristome simple, very slightly more thickened on the inner lip than 

 on the outer. The parietal wall is covered by a rather thick callus, 

 which renders the peritreme complete. Operculum typically aperos- 

 tomid, of about 8 whorls. 



The type, U.S.N.M. No. 307428, comes from Bogota, Colombia. 

 It has 4.7 whorls and measures: Height, 20,5 mm.; greater diameter, 

 38.5 mm.; lesser diameter, 27.7 mm. Height of aperture, 14.8 mm.; 

 diameter, 16.8 mm. 



This species is distinguished from all the other members of the 

 group by its very strong malleations, which lend to the surface a 

 decidedly rugose aspect. 



APEROSTOMA (APEROSTOMA) CUMINGI, new species 



Plate 31, Figubes 19-21 



Shell of medium size, depressed-helicoid, covered with a very dark 

 olivaceous-brown periostracum ; the early whorls being denuded of 

 this appear red ; interior of aperture bluish white. The nucleus con- 

 sists of 2.5 well-rounded smooth turns. Postnuclear whorls well 

 rounded, the first marked by retractively curved, somewhat irregular, 

 feeble axial riblets; the last by incremental lines and oblique scratches 

 and malleations, which render this whorl decidedly rough. Suture 

 deeply impressed. Periphery rendered angulated by a low keel, 

 which slopes more abruptly dorsally than ventrally. Base narrowly 

 umbilicated, inflated, strongly rounded, and marked like the spire, 



