254 BULLETIN 181, msTITED STATES NATIONiAL MUSEtJM 



APEROSTOMA (APEROSTOMA) MASVENSE, new species 



Plate 37, Figures 1-3 



Shell helicoid. The denuded early whorls pinkish, the rest oli- 

 vaceous with a brownish tinge. There are also irregular axial 

 streaks of a darker shade. There is a narrow light zone immediately 

 above the periphery and a broad dark band about one-fifth of the 

 width of the base anterior to the periphery. The rest of the base 

 is olivaceous horn colored; interior of the aperture bluish, showing 

 the dark band within. The nucleus consists of 2 small, well-rounded, 

 smooth turns. The postnuclear whorls are strongly rounded, the 

 last one decurrent for some little distance behind the aperture, hav- 

 ing a strongly impressed groove a little anterior to the summit. 

 The postnuclear whorls are marked by rather coarse, retractively 

 curved, and somewhat irregularly developed axial riblets, which be- 

 come decidedly weakened on the last quarter of the last turn. In 

 the groove below the suimnit there are oblique scratches. Sutures 

 very strongly impressed, almost channeled. Periphery obsoletely 

 angulated. Base narrowly openly umbilicated, inflated, strongly 

 rounded, and marked by the continuation of the axial ribs, which 

 increase but slightly on the umbilical wall. Aperture subcircular 

 with a conspicuous angulation at the posterior angle; peristome 

 simple; outer lip thin, slightly expanded; the inner lip somewhat 

 thickened. The parietal wall is covered by a thick callus, which is 

 separated from the preceding turn by an impressed line, which 

 renders the peritreme complete. 



The type, U.S.N.M. No. 524048, was collected by Oscar Haught at 

 Cerro Masve, Guayas Province, Ecuador. It has 4.5 whorls and 

 measures: Height, 18.9 mm.; greater diameter, 30.2 mm.; lesser di- 

 ameter, 21.1 mm. Height of aperture, 11.8 mm. ; diameter, 14.1 mm. 



U.S.N.M. No. 524049 contains 15 topotypes from the same source. 



The more elevated spire will readily distinguish this species from 

 A. (A.) agassizi, which also has the axial sculpture comparatively 

 stronger. 



APEROSTOMA (APEROSTOMA) AGASSIZI, new species 

 Plate 37, Figures 4-6 



Shell depressed-helicoid ; the early denuded whorls pink; the last 

 covered with a chestnut-brown periostracum, which is paler on the 

 early whorls than on the last. There is a small white zone imme- 

 diately above the periphery, and a broad dark chestnut brown band, 

 which covers about a quarter of the base immediately below the 

 periphery. The rest of the base is yellowish horn colored. The 

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



