246 BULLETIN 181, UNITE© STATES NlATTOOSIlAiL MUSEUM 



The nucleus consists of 2 small, well-rounded, smooth turns; the 

 postnuclear whorls are strongly rounded and marked by retractively 

 curved, very regular axial riblets, which are a little narrower than 

 the spaces that separate them. On the last half of the last turn the 

 riblets become less pronounced and less regular. There are also some 

 slight spiral markings on the upper surface. Suture strongly im- 

 pressed. Periphery strongly rounded. Base broadly, openly um- 

 bilicated, inflated, and marked by the continuation of the axial ribs, 

 which become a little intensified on the umbilical wall. Aperture 

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

 simple ; the outer lip of the peristome thin ; the inner slightly thick- 

 ened and reflected. The callus on the parietal wall is thick and 

 renders the peritreme complete. 



The type, U.S.N.M. No. 103999, comes from the Eich collection and 

 bears the label "Peru." It has 4.2 whorls and measures: Height, 

 14.3 mm.; greater diameter, 26.8 mm.; lesser diameter, 18.2 mm. 

 Height of aperture, 10.5 mm. ; diameter, 12.3 mm. 



This species can readily be differentiated from A. (A.) hlanche- 

 tianum (Moricand) by its lacking the narrowly channeled suture. 



APEROSTOMA (APEROSTOMA) LEAI. new species 



Plate 35, Figubes 17-19 



Shell very depressed-helicoid, almost planorbid. The upper sur- 

 face is orange horn colored, with a little lighter zone at the summit 

 and a broader white zone immediately above the periphery. The 

 base bears a broad, bright, chocolate-brown band, which covers about 

 one-third of the base anterior to the periphery. The rest is horn 

 colored, with a narrow hydrophanous band on the middle of the base. 

 Interior of aperture bluish white. The nucleus consists of 2 moder- 

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

 well rounded, the last half of the last whorl being slightly flattened 

 below the suture. The postnuclear whorls are marked by retractively 

 curved, very regular, rather closely spaced axial riblets, which are 

 separated by spaces about as wide as the axial riblets. On the last 

 part of the last turn these riblets become much enfeebled. Suture 

 deeply impressed. Periphery feebly angulated. On the dark band 

 below the periphery on the base the axial ribs are almost obsolete; 

 they grow a little stronger on the rest of the base and are strongest on 

 the umbilical wall. The umbilicus is broadly openly funnel-shaped. 

 Aperture broadly oval, with a rather strong angulation at the pos- 

 terior angle; peristome simple; outer lip thin and slightly outward 

 reflected; the inner a little thicker. The parietal wall is covered by 

 a rather thick callus which renders the peritreme complete. Oper- 

 culum typically aperostomid, showing 6 whorls remaining. 



