134 HELIX-OXYCHONA. 



and below, not descending anteriorly, angulaled in the middle ; 

 aperture oblique, trigonal, peristome expanded all around, reflexed 

 on the base, and dilated and appressed over the umbilicus and a short 

 distance on the base. Alt. 12, diam. 29 mill. 



Cordova (and Vera Cruz?) Mexico. 



H. gidllarmodi SHUTT. Bern. Mittheil. nos. 248, 249, p. 199. 

 (1852). Diagn. neuer Moll. no. 2, p. 19 (1852). PFR. in Conchyl. 

 Cab., p. 413, t. 147, f. 5-7 ; Monographia iii, p. 206. H. guillarmadi 

 KEEVE, Conch. Icon., f. 576. H. (Corasia) guillarmodi CROSSE ET 

 FISCHER, Moll. Mex. et Gaut., p. 296, t. 10, f. 8. STREBEL u. 

 PFEIFFER, Beitrag zur Kenntniss inex. L.- u. S.-wasser Conchyl. 

 pt. iv, p. 50 (1880). 



The bands continue to the edge of the peristome in H. guillarmodi, 

 while in H. trigonostoma they stop behind the expansion. 



This depressed, lens-shaped species connects the conoidal H. 

 trigonodoma with the depressed H. costaricensis. It is rather nearly 

 allied to each of these species, but is more depressed than the former, 

 and is not umbilicate like the last-named form. 



H. COSTARICENSIS Roth. PI. 18, figs. 23, 24, 25; pi. 60, figs. 1-9; 

 Vol. IV, pi. 17, figs. 38, 39, 40. 



Openly umbilicate, depressed, rather thin, white, banded above 

 with purplish or dark chestnut, base white, rarely banded, umbilicus 

 purplish or chestnut colored inside; surface shining, obliquely finely 

 striated, with traces of spiral sulci above the periphery and on base. 

 Spire depressed ; apex obtuse ; sutures linear, slightly impressed ; 

 whorls 3| to 4|, moderately convex, rapidly widening, the last 

 bluntly angulated at the periphery, descending anteriorly, convex 

 beneath, at the periphery expanded toward the peristome, on the 

 base constricted just behind it; aperture transverse, oblong or 

 trigonal, very oblique, all the margins of peristome expanded, the 

 basal margin reflexed narrowly, impinging slightly on the umbilicus. 



Alt. 12, diam. 30 mill. ; alt. 12, diam. 27 mill.; alt. 11, diam. 28 

 mill. ; alt. 10, diam. 24 mill. 



Costa Rica. 



H. costaricensis ROTH in PFEIFFER, Novitates Conchologicse i, p. 

 78, t. 21, f. 15-17; PFEIFFER, Monographia iv, p. 302. H. 

 (EpiphragmopJiord) costaricensis TRYON, Manual of Conchology, vol. 

 iv, p. 79, t. 17, f. 38-40. H. costaricensis ANGAS, Proc. Zool. Soc. 

 Lond. 1879, p. 476. H. boucardi ANGAS, Proc. Zool. Soc. Lond. 



