150 BULLETIISr 181, UTSHTEiD SfTATEISI NlATJiOiNlAIL MUStEUM 



whorls are inflated, strongly rounded, and marked by distantly 

 spaced, slender, scalariform, protractively curved axial ribs, of which 

 33 are present on the first, 29 on the second, 26 on the third and fourth, 

 and 12 on the remaining 0.4 of a turn, in the type. Suture very 

 strongly constricted. Base well rounded, very narrowly umbilicated, 

 marked by the continuation of the axial ribs. Aperture obliquely 

 oval ; peristome double, the inner expanded, thickened, exserted, and 

 slightly reflected, adnate to the preceding turn on the parietal wall. 

 There is a feeble denticle in the middle of the columella. Outer 

 peristome rather broadly flaringly expanded. 



Radula formula : 7:5:5:5. 



The type and 27 specimens. No. 140916, are in the collection of the 

 Philadelphia Academy of Natural Sciences, collected by H. B. Baker 

 at Quebrada, Venezuela. The type has almost 6 whorls and 

 measures: Height, 2.3 mm.; diameter, 1.2 mm. 



This species is distinguished from A. occideritale in having white 

 nuclear whorls, and in being stouter, with a much more strongly 

 developed peristome. 



ADELOPOMA COSTARICENSE, new species 



Plate 40, Figttke 4 



Shell minute, sinistral, thin, semitranslucent, alabaster white. 

 Nuclear whorls 1.5, inflated, strongly rounded, smooth. Postnuclear 

 whorls inflated, strongly rounded, and marked by low, lamellar, 

 scalariform, decidedly protractively slanting axial ribs, of which 24 

 are present on the first three whorls and 12 on the last half turn. 

 The spaces separating the axial ribs are 7 or 8 times as wide as the 

 ribs, and are covered by exceedingly fine, microscopic, spiral striations. 

 Suture very strongly constricted. Base inflated, well rounded, with 

 a narrow umbilical chink, marked by the continuation of the sculp- 

 ture described for the spire. Aperture broadly obliquely oval ; peri- 

 stome double, the inner strongly exserted and reflected; the outer 

 moderately broadly expanded, adnate, and appressed to the preceding 

 turn. Operculum typically adelopomid. 



The type, U.S.N.M. No. 516034, comes from Santa Maria, Costa 

 Rica, at an altitude of 1,550 meters. It has 6 whorls and measures : 

 Height, 2.3 mm.; diameter, 1.2 mm. U.S.N.M. No. 516035 contains 

 9 topotypes. 



This species is distinguished from A. occidentale (Guppy) by being 

 a little slenderer and having fewer axial ribs; these, too, are less 

 worn at the summit and near the periphery than on the middle, which 

 is not true of occidentale. 



