1892.] NATURAL SCIENCES OF PHILADELPHIA. 341 



outer lip not sinuous ; inner lip more or less heavily calloused, 

 not notched at the base. Operculum few-whorled, with basal nucleus. 

 Type P. Rovirosai Pils. 



This group has the sculpture of Hemisinus but differs from that 

 genus in the entire, un-notched basal lip. The columella callus is 

 much like some species of Pachychilus but the operculum is very 

 different from that genus. From both of these groups it differs in 

 the short, ovate contour of the shell. The description of the oper- 

 culum is taken from Melania brevis d'Orbigny of Cuba, which I con- 

 sider congeneric. 

 P. Rovirosai n. sp. (PI. XIV, figs. 8, 9.) 



Shell oblong-conic, very solid, whitish, encircled by numerous nar- 

 row smooth spii'al line of a dark brown color, and somewhat 

 alternating in size. Spire conical, apical whorl eroded ; whorls 5 

 remaining, slightly convex, the last whorl large, regularly convex. 

 Aperture a little less than half the length of the shell, ovate, angular 

 above; outer lip regularly arcuate; inner lip strongly calloused. 



Alt. 20, diam. 12 mill, (old specimen.) 



Alt. 16 J, diam. 91 mill, (young specimen.) 



Two specimens are before me, collected by Prof Rovirosa at the 

 mountains of Poana, State of Tabasco. The older individual (PL 

 XIV, fig. 8) is considerably worn ; the other is perfect but not 

 whollv adult, and neither contains the operculum. The species is 

 allied, apparently, to the Cuban Melania brevis Orb., but is 

 decidedly longer, and the lira; are much stronger. 



The relationship of Potamanax to Hemisinus in sculpture and 

 operculum is obvious, and has caused me to regard it as a subgenus 

 rather than a distinct genus ; but the total lack of a basal notch or 

 truncation is a character usually considered of generic importance. 



Explanation of Plate XIV. 



Figs. 1, 2, 3, Chrysodormis (Sipho) Stonei Pils. 



Fig. 4, Eucalodium eompactum Pils. 



Fig. 5, 6, Pachychilus glaphyrus var. 



Fig. 7, P. glaphyrus var. potamarchus Pils. 



Figs. 8, 9, Potamanax Eovirosai Pils. 



