PILSBRY: non-marine MOLLUSCA of PATAGONIA. 563 



POTAMOPYRGUS SCOTTII Sp. IIOV. 

 (Plate XLlc, Figs. 10, 11.) 



The shell is very minutely perforate, turritc, the length about double 

 the greatest diameter and nearly three times the length of the aperture. The 

 spire has straight outlines and an obtuse apex. Whorls Gyi , very convex, 

 parted by a deep suture. The first two whorls are smooth ; then fine, 

 narrow, thread-like, spiral striae appear, 6 to 8 in number on the visible 

 part of each whorl, one at the upper third sometimes being more promi- 

 nent. There are also numerous ripples in an axial direction, on the last 

 two whorls. The last whorl is well rounded and nearly smooth on the 

 base. The aperture is ovate, peristome simple and thin, continuous, the 

 columellar margin concave, narrowly reflexed. 



Fig. 10. Length 5, diam. 2.6, length of aperture 1.7 mm. 

 " II. " 3.8 " 1.9 " " 1-4 " 



Buenos Aires. Types No. 10,153 A. N. S. P. 



This is a very much lengthened form, larger and longer than P. gitara- 

 nitictis (Doer.), and differs in sculpture. It is closely related to P. peten- 

 ingensis (Gld.) which, however, has a smooth surface. The specimens 

 are bleached and apparently fossil, being filled with sandy mud. A 

 minute embryonic shell was obtained from the matrix washed out of one 

 of the specimens figured. This confirms the generic reference to some 

 extent, as all Potamopyrgns species are viviparous. 



Named for Professor W. B. Scott, whose work has thrown a flood of 

 light on Patagonian vertebrate palaeontology. 



POTAMOPYRGUS PETENINGENSIS (Gould). 

 (Plate XLIr, Fig. 12.) 



Cingu/a peteiiiiigensis Gon\d,\J. S. Expl. Exped., Mollusca, p. 130, pi. 

 9, figs. 152, a, b. 



Lagoa de Peteninga, near the entrance of Rio Janeiro harbor, in brackish 

 water. 



The shell of this species resembles Paliidestrina attenuata of the eastern 

 United States by its extremely convex whorls parted by deep sutures. 

 The type, from the Lagoa de Peteninga, was described as smooth, about 

 8.5 mm. long, 2.5 wide, with 6 whorls. One of the original lot is figured 



