1856.] 123 



If distinct ; aperture sub-quadrate, or rounded ovate, more angular above, broad- 

 ly rounded below ; lip thin, reflexed on the colutnf-llar side below, but leaving a 

 small umbilical groove; columella strongly arcuate. Length -S*] inch; breadth 

 73 inch ; apical angle convex, divergence 73 to 77. ^ 



This interesting shell is so unlike the usual forms of PalUdina, that we would 

 have referred it to that genus with much doubt, had it not been for the fact that 

 we have from the same bed some intermediate gradations between it and the 

 risual typical forms of the genus. One of these, P. Leidyi of ih'S paper must be 

 (judging from the upper volutions,) in its young state, almost exactly like this, 

 both in form and surlace markings, yet at maturity, its last volution loses 

 almost entirely the angular outline characterizing this species at all stages of its 

 growth. We have seen fragments of this species indicating a size at least three 

 times as great as that of the specimen from which the above measurements were 

 taken. 



P. cingulata of Matheron (see Catalogue Methodique, &c., p. 223,) from the 

 Lignite formations near the mouth of the Rhone, resembles this more than any 

 fossil species with which we are acquainted, but ditFersin the surface markings. 

 Amongst recent species it has two or three closely allied representatives, now in- 

 Ijahitingthe rivers of China and Siam, of which P. pyrimidata (Phillippi) is an 

 exam [lie. 



LoculHy. Ten miles below Fort Union. 



Palt'dina Leidyi. 



Shell very large, conical-ovate, oblique, thin ; spire elevated ; upper volutiona 

 flattened, and ornamented by two indistinct revolving ridges ; lower ones more 

 rounded, last rather ventri-ose, and obscurely angular below ; suture linear and 

 scarcely distinct above, but well defined between the lower whorls ; surface 

 marke(l with distinct lines of growth, crossed by very fine, elevated revolving 

 lines, generally obsolete on the lower volutions; aperture apparently ovate; in- 

 ner lip spread upon the body whorl, but leaving partly uncovered a small, d(!ep, 

 oblique umbilical pit. Length about 1 86 inches; breadth 1-32 inches; apical 

 angle convex, divergence 65. 



The most remarkable ftatures about this fine Paludina, are is large size, and 

 the peculi'irity of having the lower volutions smoothly rounded, or more or less 

 convex, while those nearest the apex are flattened and ornamented by two ob- 

 scure revolving ridges. The angle on the lower part of the last whorl is very- 

 obscure near the aperture, but becomis more distinct higher up, and must be 

 quite conspicuous on young shells. Unfortunately we have no specimens with 

 the aperture entire. (Jnr best specimen consists of four volutions, and judging 

 from the appearance of the broken apex, it must have had about two more. 



We name this species after Prof Joseph Leidy, of the University of Pennsyl- 

 vania. 



Localiiij. Ten miles below Fort Union. 



Valvata parvula. 



Shell very small, much depressed or subdiscoidal ; spire rising little above 

 the body whorl ^ volutions about three, nearly cylindrical, and having near the 

 middle, on the upper and lower sides, a distinct linear carina ; surface marked 

 with strong regular lines of growth ; sutures distinct ; umbilicus wide and deep, 

 showing all the volutions to the apex, aperture round or transversely oval. 

 Height .05 inch ; breadth .10 inch. 



Frnm V. tricarinata (Say,) some varieties of which this resembles more than 

 any spec es known to us, it differs in having a wider umbilicus, less elevated 

 spire, and much stronger lines of growth. 



Localvy. Three miles below Fort Union. 



Melania minutdla. 

 Shell minute, elongate conical ; volutions seven to seven and a hilf, convex, 

 increasine gradually from the apex and flattened obliquely outwsrd fiom above, 

 near two-thirds of the way down, whence they round abruptly in to the suture 



