260 BULLETIN 181, UNITElD STIATES NATIONAL MUSEUM 



strong on the umbilical wall. Aperture circular with a slight angu- 

 lation at the posterior angle; peristome simple; outer lip thin and 

 the inner slightly thickened. The parietal wall is covered by a 

 moderately strong callus M'hich renders the peritreme complete. 



U.S.N.M, No. 316104 contains two specimens from Quito, Ecuador. 

 The one figured has 4 whorls and measures: Height, 13.8 mm.; 

 greater diameter, 24,5 mm.; lesser diameter, 16.8 mm. Height of 

 aperture, 10.2 mm. ; diameter, 11.1 mm. 



The small size and more depressed form readily distinguish this 

 species from A. (A.) colojnbieiise (Da Costa), and the regular rib- 

 bing of the upper surface differentiates it from A. {A.) redfieldi. 



APEROSTOMA (APEROSTOMA) BOLIVIENSE, new species 



Plate 38, Figures 7-9 



Shell helicoid, covered with a chestnut-brown periostracum, which 

 is a little paler near the suture than on the major portion of the 

 turns. There is a narrow, inconspicuous, lighter zone immediately 

 above the periphery. The base is marked by a broad chestnut- 

 brown band, which gradually fades from the periphery basally. This 

 is separated by a narrow band, which is about twice as wide a.s 

 the narrow dark chestnut-brown band below it, which occupies 

 the middle of the base. The general coloration of the base is oliva- 

 ceous horn colored; interior of aperture bluish white. The nucleus 

 consists of 2 small, well-rounded, smooth turns. The postnuclear 

 whorls are strongly rounded; the summit of the last one gradually 

 falls below the periphery of the preceding turn. The postnuclear 

 whorls are marked by rather strong, retractively curved axial riblets, 

 which grow somewhat weaker and irregular on the last part of 

 the last whorl. Suture very deeply impressed. Periphery obsoletely 

 angulated. Base narrowly umbilicated, inflated, strongly rounded 

 and marked by the continuation of the axial ribs, which grow very 

 slightly stronger on the umbilical wall. Aperture broadly oval, pro- 

 duced at the junction of the basal and outer lip; peristome simple; 

 outer lip sharp; inner somewhat thickened. The parietal wall is 

 covered by a thick callus, which is separated from the preceding 

 turn by a deeply impressed groove which renders the peritreme 

 complete. 



The type, U.S.N.M. No. 307426, was received from Sowerby and 

 Fulton with the designation '-'-Neocyclotus inca Orbigny var. Minor 

 Pfeiffer" and the locality "Bolivia." It has 4.2 whorls and measures : 

 Height, 14.5 mm.; greater diameter, 23.9 mm.; lesser diameter, 16.5 

 mm. Height of aperture, 9.7 mm.; diameter, 10.9 mm. 



U.S.N.M. No. 524102 contains one topotype from the same source. 



