140 HELIX-ISOMERIA. 



perisiome white, moderately thick ; basal margin with two incon- 

 spicuous tubercles; columellar margin very short, thicker, partly 

 covering the umbilicus. 



Alt. 16 to 17, diam. maj. 35 to 38, diam. min. 30 to 31 mill. 



Aperture, breadth 15 to 16, alt. 12 to 13 mill (Measured inside 

 peristome.) 



Canton of Megia, Prov. Pichincha, Ecuador. 



Isomeria aloagana Jouss., Bull. Soc. Zool. France, xii, 1887, p. 

 179. 



The above description is somewhat shortened from that of 

 Jousseaume. 



H. PERITROPIS Pilsbry. PL 63, figs. 10-13. 



Umbilicate, rather thin, depressed, lens-shaped carinated at the 

 circumference, convex above and beneath, chestnut colored. The 

 surface is shining, closely obliquely striate, the strise stronger above,, 

 granulate (under a lens), the granulation more or less obsolete, 

 especially on the whorls of the spire. The spire is low-conoidal, its 

 lateral outlines a trifle convex ; apex obtuse, corneous, first two 

 whorls minutely granulate, not striate ; sutures linear or a trifle im- 

 pressed. Whorls 5 or 5J, slowly, regularly Avidening, nearly plane 

 or a little convex ; the last whorl is not oblong nor transversely 

 dilated, but is a trifle narrower toward its latter fourth (seen from 

 above) ; it is depressed, acutely keeled, somewhat convex beneath ; 

 the carina is subobsolete on the last fourth of the whorl. At the 

 aperture the whorl is abruptly deflexed, descending only a short 

 distance (1 to 2 mill.) ; behind the peristome it is constricted. The 

 aperture is subtrigonal, livid inside. The peristome is expanded, 

 subreflexed, rather narrow and thin, white ; the outer portion is 

 labiate with chestnut color inside ; outer and upper portions arcuate, 

 basal lip straight, rather abruptly curving at the columellar insertion, 

 where it is a trifle dilated, and connected with the upper margin of 

 peristome by a cord-like white ridge of callous, which is either 

 straight or curves outward a little. There are no lip-teeth ; the 

 parietal wall of aperture bears a minute oblique denticle. The 

 umbilicus is large (4 to 5 mill, diam.) and deep ; it expands behind 

 the peristome, and has an obsolete spiral furrow there, and stronger 

 radiating striae. 



Alt. 15, diam. maj. 34, min. 30 mill. 



Alt. 14, diam. maj. 33, min. 29 mill. 



Bogota, Colombia. 



