602 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



Uruguay River, at Paysandu, Uruguay. Types, No. 103,050, A. N. S. P. 



Development. — The smallest specimens seen measure 3 mm. diam., 

 2.8 high. The peripheral flattening is already weakly perceptible. There 

 is no trace of a basal angle or columellar area, but the columella is very 

 wide, almost semicircular, with a deep excavation in its face. The angle 

 bounding the columellar area is developed very late, appearing only on 

 the last whorl. 



This species is described from four specimens, none of them perhaps 

 completely mature. The shell figured is almost mature, but lacks the 

 post-variceal contraction of the lip, which would probably be acquired. 

 Two of the shells have a peripheral brown band, fading out at the edges, 

 and one has a second fainter band on the outer part of the base. 



Compared with P. i/ieniigi, this species differs by its somewhat biangular 

 shape, the lower varix and the coloration. P. paysanduanus differs more 

 radically by its columella. 



LITHOCOCCUS gen. nov. 



Shell globose, thick, sculptured with strongly developed spiral ribs, the 

 upper ones spinose ; composed of 4 to 5 convex whorls. Operculum cor- 

 neous, subcircular, composed of 3 or 4 whorls, the nucleus near the cen- 

 ter. Dentition Amnicoloid ; central tooth with 5 to 7 denticles on the 

 cusp and 3 basal denticles on each side. Inner lateral tooth with 13-14, 

 next with about 16 denticles. Type L. Diulticariuatus. 



This genus differs from the LithoglypJiince and Potamolithus by the 

 operculum. The penis has not been examined. 

 LiTHOCOCCUS MULTiCARiNATUS (Miller). LithoglypJuis mnlticarinatus 



Miller, Malakozoologische Blatter, n. F., I, p. 157, Taf 15, f 4. Rio 



Cayapas, Ecuador, abundant on rocks. 



PELECYPODA. 



Family SPHyERIID^ Ball. 



The family SpJicsriida; is represented in South America by four genera : 

 Sphcerimn, Mitsciilium, Enpera and Pisidiuui. Doubtless the last two 

 genera will prove to be generally distributed and numerous in forms, 

 Enpera in tropical, Pisidinm in temperate and cold regions ; but up to this 

 time only a few have been described. The list of species described from 



