240 BULLiETIlN 181, UNITE© STATES ISnATTOlNlAiL MUSEUM 



smooth turns; the postnuclear whorls are moderately rounded, 

 slightly flattened near the summit, the last one for about one-tenth of 

 a turn forming a cord at the appressed summit. The postnuclear 

 whorls are marked by fine, retractively curved axial riblets which are 

 about as wide as the spaces that separate them but which become ir- 

 regular and less developed on the last turn, particularly toward the 

 aperture. Suture well impressed. Periphery feebly angulated. 

 Base openly umbilicated, inflated, well rounded, and marked by the 

 continuation of the axial riblets, which extend over the umbilical 

 wall, where they become somewhat strengthened. Aperture subcir- 

 cular, decidedly protracted at the posterior angle into an auricle, 

 which bears a groove in its middle; peristome simple; the outer lip 

 sharp and somewhat reflected; the inner somewhat thickened. The 

 parietal wall is covered by a thick callus, which renders the peritreme 

 complete. There is only a feeble inclination toward an inbending 

 at the junction of the columella with the parietal wall. Operculum 

 typically aperostomid, showing 9 whorls. 



The specimen described and figured, U.S.N.M. No. 307424, comes 

 from New Grenada. It has 4.9 whorls and measures: Height, 27.5 

 mm. ; greater diameter, 47 mm. ; lesser diameter, 32.4 mm. Height of 

 aperture, 17 mm. ; diameter, 22.8 mm. 



U.S.N.M. No. 307421 contains one specimen from Quito, Ecuador. 



This species can readily be distinguished from .4. (A.) ut'Haense 

 by its deflected last whorl. 



APEROSTOMA (APEROSTOMA) UTRIAENSE, new species 



Plate 34, FiGimEs 4-6 



Shell of medium size, depressed-helicoid. The upper surface is 

 covered with a pale chestnut-brown periostracum, but there is a rather 

 broad paler area immediately below the summit. There is also a light 

 zone immediately above the periphery, while a broad chestnut-colored 

 band extends over the posterior two-fifths of the base, the rest being 

 pale olivaceous horn colored ; interior of aperture bluish white. The 

 nuclear whorls in the type are lost. The postnuclear whorls are well 

 rounded and on the last turn there is a groove immediately below the 

 periphery. The postnuclear whorls are marked by very fine, closely 

 spaced, retractively slanting axial riblets, which become much weak- 

 ened on the last whorl. Suture strongly impressed. Periphery well 

 rounded. Base moderately broadly openly umbilicated, marked by the 

 continuation of the axial sculpture, but much more roughly so. The 

 axial ribs of the base become fused into stronger elements on the um- 

 bilical wall. Aperture subcircular, with a moderately strong angula- 

 tion at the posterior angle, which bears a median groove; outer lip 

 thin and somewhat reflected; the inner lip slightly thickened. The 



