1856.] / 121 



pressed ; surface ornamented by more or less distinct lines of growtli, which are 

 crossed by numerous small, thread-like, revolving lines ; aperture comparatively 

 small, obliquely-ovate ; inner lip thin and reflexed below so as to partly cover 

 the small umbilical perforation. Length 1 inch ; breadth .71 inch ; length of 

 aperture .47 inch ; apical angle convex, divergence 54 to 60. 



Sometimes the lower volution, which generally forms less than half the entire 

 length of the shell, is slightly flattened above the middle, so as to leave an ob- 

 scure angle a little below the suture. On the upper half of the volutions the 

 revolving lines are separated by spaces from two to five times their width, but 

 decrease in size and become closely crowded on the lower part of the last whorl, 

 excepting near the umbilicus, where they are again stronger, more distant, and 

 minutely flexuous. On worn specimens the revolving lines are often obscure. 



Locality. Fort Clark. 



Paludina vetula. 



Shell conical-ovate, not very thick ; spire relatively small, moderately elevated; 

 volutions about five and a half, convex, narrow, increasing gradually from the 

 apex, last one large and ventricose ; surface marked with fine lines of growth, 

 which are crossed by obscure revolving lines ; suture strongly impressed, very 

 slightly oblique ; aperture narrow ovate ; umbilical perforation closed or \cvj 

 small. Length about .81 inch ; breadth .60 inch ; length of aperture .40 inch ; 

 breadth of do. .24 inch ; apical angle nearly regular, divergence 60. 



Associated with this species a few specimens about one third larger were found, 

 which have a more elevated spire, in consequence of which the divergence of 

 the apical angle is some four or five degrees less. The revolving lines also ap- 

 pear stronger. It is very difficult to determine, without a larger number of in- 

 dividuals in a better state of preservation, whether they are a variety of this 

 species or whether they may not be identical with the last. It is even possible a 

 more extensive collection may prove both these to be only varieties of the last, 

 though as we now see them, they present quite a different aspect, especially the 

 smaller variety, which has a more slender and much less elevated spire, with 

 more depressed whorls, smaller umbilical perforation, and much less distinct re- 

 volving lines. The body whorl is also relatively larger and much more extended 

 below. 



Locality. Bad Lands of the Judith. 



Paludina Leai. 



Shell conical-ovate, oblique ; spire not much elevated, pointed at the apex , 

 volutions five and a half to six, convex, sometimes ventricose, last one obscurely 

 angular below the middle ; suture well defined ; surface marked with fine lines 

 of growth, which are crossed by extremely fine, nearly obsolete revolving striae, 

 and at regular intervals by revolving rows of minute, shallow punctffi ; aperture 

 broad ovate, obtusely angular above, rounded below ; outer lip thin ; inner lip 

 thin above, thicker and slightly reflexed below the small umbilical pit ; columella 

 deeply arcuate. Length .97 inch ; breadth .75 inch ; length of aperture .47 inch ; 

 breadth of do. .40 inch ; apical angle convex, divergence 65 to 80. 



This shell varies so greatly in the elevation of its spire, and the divergence of 

 its apical angle, that its varieties might be mistaken for three or four distinct 

 species. We have satisfied ourselves, however, by examining a large number of 

 specimens, that all these varieties are connected by a regular series of interme- 

 diate forms. In some individuals the upper volutions are slightly flattened on 

 top immediately below the suture, in others they are rounded convex, while in 

 a few instances all the whorls are more or less depressed, so as to give the shell 

 a subtrochiform aspect. Generally the fine revolving stria3 and rows of minute 

 punctae are nearly obsolete, and they are never visible without the aid of a good 

 lens. 



It is an interesting fact that this species is so nearly allied, both in form and 

 surface markings, to a Paludina now inhabiting the streams of Southern Asia, 

 {P. Bengalensis, of Lea) as to give rise to a doubt whether or not they really are 



