THE CYCIiOPHORTD LAND M0LLU6K9 OF AMERICA 249 



posterior angle ; peristome simple ; outer lip thin, the inner thickened 

 and slightly reflected. A strong callus covers the parietal wall and 

 renders the peritreme complete. The operculum is typically aper- 

 ostomid and shows 8 whorls. 



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

 Ecuador. It has 4.6 whorls and measures : Height, 23.3 mm. ; greater 

 diameter, 33.0 mm.; lesser diameter, 25.5 mm. Height of aperture, 

 14.5 mm.; diameter, 15.7 mm. 



U.S.N.M. No. 307407 contains three topotypes, and U.S.N.M. No. 

 316110 contains another topotype. 



This species is differentiated from the others of the group that 

 have the axial ribs of the umbilical wall stronger than on the upper 

 surface by its narrow umbilicus. 



APEROSTOMA (APEROSTOMA) SUBCINGULATUM (Kobclt) 



Plate 36, Figubes 1-3 



1912. Neocpclotus (giganteus?) subcingulatus Kobelt, Martini-Chemnitz Con- 



chylien Cabinet, vol. 1, sect. 19, pt. 3, p. 892, pi. 133, figs. 4-6. 

 1923. Poteria (Neocyclotus) subcingulatum H. B. Baker, Occ. Pap. Mus. Zool. 

 Univ. Michigan, No. 137, p. 42. 



Shell low, helicoid, covered with a reddish periostracum, which 

 pales to chestnut-brown on the last turn. There is a very narrow 

 light zone immediately above the periphery. The base is bicolor ; the 

 posterior portion covering about two-fifths of the base is dark chest- 

 nut-brown at the periphery and gradually pales anteriorly; the an- 

 terior portion is bright horn color. The nucleus consists of 2 small, 

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

 the last one having a slight depression immediately below the sum- 

 mit. All but the last postnuclear whorls are marked by slender, 

 retractively curved axial riblets, which are not so wide as the spaces 

 that separate them. On the last whorl, however, these riblets grow 

 consecutively weaker and become quite evanescent toward the end. 

 Suture very strongly impressed. Periphery well rounded. Base 

 broadly umbilicated, inflated, marked by the continuation of the axial 

 riblets, which are weak at the periphery but grow stronger as they 

 cross the base, being very strong on the umbilical wall. Aperture 

 broadly oval, with a slight auricle at the posterior angle; peristome 

 simple; the outer lip thin; the inner lip slightly thickened and 

 slightly reflected. The parietal wall is covered by a moderately thick 

 callus, which renders the peritreme complete. 



The specimen described and figured, U.S.N.M. No. 98109, comes 

 from Quito, Ecuador. It has 4.6 whorls and measures : Height, 19.5 

 mm. ; greater diameter, 36.1 mm. ; lesser diameter, 24.6 mm. Height 

 of aperture, 14.7 mm. ; diameter, 16.3 mm. 



