194 BTJLLiETllN 181, UNITED STATES NIATTO'NiAiL MUSEUM 



marked by irregular and irregularly depressed axial riblets, which 

 vary both in strength and spacing. Suture deeply impressed. Periph- 

 ery weakly angulated. Base openly umbilicated, strongly rounded^ 

 and marked by the continuation of the axial riblets, which become 

 stronger and more distinct on the umbilical wall. Aperture almost 

 circular, produced into an auricle at the posterior angle; peristome 

 simple, the inner thickened; the outer thin and sharp. The last whorl 

 descends below the periphery and so does the tip of the auricle. 



The type, U.S.N.M. No. 380795, was collected by R. H. Palmer in a 

 dense jungle 13 km. south of Puerta Santos, Province of Santander 

 del Norte, Colombia. It has 4.5 whorls and measures: Height, 19.2 

 mm. ; greater diameter, 36.5 mm. ; lesser diameter, 25.6 mm. Height of 

 aperture, 14.8 mm. ; diameter, 15.8 mm. 



This species recalls A. (/.) hitomi from Peru but has the axial ribs 

 much less regular and the suture much more deeply channeled. The 

 small aperture distinguishes it from A. (/.) jnzar?^. 



APEROSTOMA (INCIDOSTOMA) HITOMI, new species 

 Plate 27, Figubes 26-28 



Shell depressed-helicoid. The early denuded whorls are pale rose 

 color ; the last whorl is covered by a thin periostracum, which is pale 

 olivaceous horn colored on the upper surface and a trifle darker on 

 the base. It has a rather broad light zone immediately above 

 the periphery and a dark zone a little narrower than the pale one 

 below the periphery, the dark zone fading anteriorly into the general 

 coloration of the base. The nucleus consists of about 2 whorls, small, 

 well rounded, smooth. The postnuclear whorls are well rounded and 

 marked by very regular, rather closely spaced, decidedly retractively 

 curved axial riblets. The spaces that separate these riblets are about 

 as wide as the riblets. On the upper surface near the aperture there 

 are also some oblique scratches. The summit of the turns is appressed 

 to the suture and creeps but slightly on the preceding turn ; the suture 

 therefore is not channeled. The periphery is well rounded; the 

 white band, however, gives it the appearance of an angulation, which 

 is an optical illusion. Base well rounded, moderately openly um- 

 bilicated, and marked by the continuation of the axial riblets, which 

 become stronger on the umbilical wall. Aperture circular, produced 

 into an auricle at the posterior angle ; peristome simple, the inner lip 

 thickened, the outer thin, except at the posterior angle, where it be- 

 comes thickened and bent inward over the aperture as a slight hood. 



The type, U.S.N.M. No. 316105, was collected by Cuming at Quito, 

 Ecuador. It has 4.7 whorls and measures : Height, 21.7 mm. ; greater 

 diameter, 39.2 mm. ; lesser diameter, 27 mm. Height of aperture, 14.6 

 mm. : diameter, 17.0 mm. 



