1G4 [August, 



Mytilus Galpinianus . (Nov. sp.) 



Shell sub-ovate, arcuate, inflated, surface smooth, or marked only by five in- 

 distinct concentric lines of growth ; umbones prominent, rounded, anterior side 

 short; beaks nearly terminal, muscular impression small, placed near the an- 

 terior extremity ; posterior side broad, extremity rounded. 



Dimensions. Length 7.5 lines, width 15 lines, thickness 6 lines. The only 

 specimen we have of this species is partly denuded of its shell, so that some of 

 the characters above given may have to be slightly modified, when more perfect 

 specimens are obtained for examination. 



Locality. Fox Hills, Nebraska. For this species we are indebted to the 

 politeness of Mr. Galpin, agent of the Amer. Fur Co., in charge of Fort Pierre 

 Chouteau, and to him it gives us pleasure to dedicate it. 



Pholadomya elegantula. (Nov. sp.) 



Shell sub-ovate, transverse, inflated; anterior side short, rounded ; posterior 

 side elongated, gaping; basal margin regularly rounded ; ligament margin arcu- 

 ate ; umbones prominent ; surface marked with about 45 concentric ribs, which 

 increase in width from the beak to the fyasal margin, becoming nearly obsolete 

 posteriorly ; these are crossed by about 25 radiating granular ribs, close together 

 on the middle portion of the shell, the intervals increasing in width towards the 

 anterior and posterior borders. 



Dimensions. Length 18 lines, width 22 lines, thickness 1 inch. 



Locality. It occurs in septaria of the cretaceous group at Sage Creek, Ne- 

 braska, associated with Ammonites Oweni 9 Scaphites nodosus and Inoceramus 

 Sagensis. 



Rostellaria Nebrascensis. (Nov. sp.) 



Shell elongate, conical ; whorls about eight, convex, body whorl with two well 

 rounded keels ; lip prolonged transversely, terminating in a sharp point ; all the 

 volutions ornamented with transverse revolving thread-like striae, which are 

 crossed longitudinally by prominent flexuous ribs. 



It occurs with the preceding species at Sage Creek, Nebraska. 



Descriptions of neiv fossil species from the fresh water Tertiary Formation of Ne- 

 braska, collected by the North Pacific Railroad Expedition, under Gov* J J 

 Stevens. 



By John Evans, M. D., and B. F. Shumard, M. D. 



The organic remains which form the subject of the present communication 

 were obtained from Nebraska Territory, in the vicinity of Peno Creek, a small 

 tributary of Teton or Little Missouri River, about ninety miles from Fort 

 Pierre Chouteau. They occur in great profusion in thin-bedded, light gray, sili- 

 ceous limestone, near the summit of the elevated plateaux which border the 

 Mauvaises Terres. They consist of several species of Lymnea, one Physa, one 

 Planorbisy the seed vessels of a species of Chara and the carapaces of a minute 

 Cypris. These genera at once establish the lacustrine character of the deposit 

 in which they occur. The fossils are beautifully preserved, and project in fine 

 relief from the weathered surfaces of the limestone. Many of them have been 

 converted into semi-transparent chalcedony. They are of considerable interest, 

 from the fact, that the strain in which they are imbedded, repose on the tertiary 

 marls and clays, which have yielded those magnificent collections of extinct mam- 

 malian and chelonian remains de^ribed by Prof. J. Leidy, in his recent very 

 valuable memoirs, published in Dr. Owen's Final Report on the Geology of 

 Iowa, Wisconsin and Minnesota, the Smithsonian Contributions, and in the Pro- 

 ceedings of the Academy of Natural Sciences. 



Planorbis Nebrascensis. (Nov. sp.) 

 Shell small, depressed, discoidal, above moderately concave ; volutions about 

 four, rounded, obtusely carinated ; below rounded, umbilicus small, exhibiting 

 the volutions to the apex of the spire, suture distinct ; body whorl with an obtuse 



