248 BULLETM ISl, UNITE© SITATES NiATIONlAI. MUSEUM 



Shell very depressed-helicoid, almost planorbid, covered by an 

 olivaceous periostracum, with a moderately broad light zone immedi- 

 ately above the periphery and the posterior half of the base oliva- 

 ceous-chestnut colored ; the anterior half and the umbilicus are horn 

 colored; interior of aperture bluish white. The nucleus consists of 

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

 slightly rounded with a depression a little below the summit on the 

 last half of the last turn. The postnuclear whorls are marked by 

 obsolete, retractively curved axial riblets and faint traces of mallea- 

 tions in the depressed portion below the summit. Suture very 

 strongly impressed. Periphery well rounded. Base broadly, openly 

 umbilicated, inflated, well rounded, and marked by rather regular 

 axial riblets, which become intensified on the umbilical wall. Aper- 

 ture circular with an angulation at the posterior angle; peristome 

 srniple ; the outer lip thin, the inner thin and slightly reflected. The 

 parietal wall is covered with a thin callus rendering the peritreme 

 complete. Operculum typically aperostomid, showing 8 whorls. 



U.S.N.M. No. 25074:2 contains two specimens from Chanchamayo, 

 Peru. The specimen described and figured has 4.5 whorls and meas- 

 ures : Height, 13.8 mm. ; greater diameter, 26.4 mm, ; lesser diameter, 

 19.5 mm. Height of aperture, 11 mm. ; diameter, 12 mm. 



This species resembles A. (A.) venezuelense in the obsolete ribbing, 

 but differs from it in having the whorls much flatter on the upper 

 surface and not inbent near the suture as in that form. 



APEROSTOMA (APEROSTOMA) ECUADORENSE, new species 



Plate 36, Figures 4-6 



Shell helicoid, the early whorls reddish horn colored, the last horn 

 colored. There is a lighter, very pronounced zone immediately above 

 the periphery, and a darker zone, which gradually fades basally, 

 occupying the posterior two-fifths of the whorl. The rest of the base 

 is of about the same shade of horn color as the last whorl; interior 

 of aperture bluish white, showing the external banding within. The 

 nucleus consists of 2 moderately large, well-rounded, smooth turns. 

 The postnuclear whorls are well rounded; the last one is gradually 

 deflected for half of a turn. The postnuclear whorls are marked by 

 quite regular, retractively curved, slightly flattened axial riblets, 

 which are a little broader than the spaces that separate them. On 

 the last part of the last turn these become somewhat weakened. 

 Suture well impressed. Periphery rounded. Base narrowly um- 

 bilicated, inflated, strongly rounded, and marked by strong axial 

 riblets, which are considerably stronger than those on the upper sur- 

 face. Aperture oblique, subcircular, with a slight auricle at the 



