HELIX-ISOMERIA. 157 



H. SUBCASTANEA Pfeiffer. PI. 44, figs. 8, 9, 10. 



Umbilicate, depressed-orbicular, chestnut-colored, with a narrow 

 whitish or yellowish peripheral fascia; solid ; surface lightly, 

 irregularly obliquely striate, microscopically granulated, shining, 

 spire convex ; sutures slightly impressed. Whorls 5, the apical 1 

 nearly planorboid, convex, whitish-corneous, the remainder slightly 

 convex, slowly widening, the last angular at the periphery, deflexed 

 anteriorly, deeply constricted on the base behind the peristome, and 

 near the periphery with a deep pit, its sides rugose ; aperture very 

 oblique, livid inside; peristome broadly expanded, white, basal 

 margin reflexed, bearing at its junction with the outer margin a 

 large strong, entering, compressed tooth, situated on an eminence of 

 the basal shell-wall causing a pit behind the peristome ; basal mar- 

 gin subsinuous within, calloused in the middle, at its insertion half- 

 covering the umbilicus. 



Alt. 22, diam. maj. 41, min. 34 mill. 

 Alt. 23, diam. maj. 44, min. 37 mill. 

 Alt. 23, diam. maj. 50, min. 43 mill. 



S. W. Colombia; N. W. Ecuador. 



Carocolla globosa BRODERIP, Proc. Zool. Soc. Lond. 1832, p. 30 

 (not H. globosus Sowerby, Mineral Conchology, ii, p. 157, pi. 170, 

 1818 ; see, also, on this species, Edwards, Monogr. Moll. Eocene of 

 England, p. 63, t. 10, f. 2 ; and Sandberger, Land- u. Siisswasser 

 Conchyl. der Vorwelt, p. 291, 1. 17, f. 3). H. subcastanea PFEIFFER, 

 Symbolse, ii, p. 103 ; Monographia, i, p. 401. REEVE, Conch. Icon., 

 f. 543. Isomeria subcastanea MILLER, Malak. Blatter 1878, p. 

 170. 



Known from other species by the single large compressed tooth at 

 junction of outer and basal lips, marked behind the peristome by 

 a deep pit. 



The typical form is that figured by Reeve (pi. 44, fig. 10 of this 

 volume) ; the upper lip is arcuate; a larger, more depressed speci- 

 men, with horizontal, subsinuous superior lip is figured on pi. 44, 

 figs. 8, 9. 



* * * 



The following species form a group intermediate between Isomeria 

 and Labyrinthus in appearance, differing from the former in having 

 the teeth more strongly developed, especially the parietal fold, and 

 from the latter in the subglobose-depressed form and oblong, trans- 

 versely dilated outline. 



