NATURAL SCIENCES OF PHILADELPHIA. 175 



Descriptions of new Organic Remains from the Tertiary, Cretaceous and 

 Jurassic Rocks of Nebraska. 



BY F. B. MEEK AND F. V. HAYDEN. 



The following new species of fossil raollusca, belong mainly to the collections 

 brought from Nebraska by the expeditions under the command of Lieut. G. K. 

 Warren, of the U. S. Top. Engrs. in 185(3-7 and 8. More extended descriptions 

 of these and the other species already described by us from that region, together 

 with remarks, comparisons, and full illustrations, will appear in Lieut. War- 

 ren's final report. 



TERTIARY SPECIES. 



GASTEROPODA. 



Helix Evansi, A. k H. Shell small, suborbicular, spire depressed ; volu- 

 tions four and a half to five, obliquely compressed, or a little convex above, 

 rounded on the outer side, and very convex below, the most prominent part being 

 near the umbilicus, concave within, and each embracing on the upper side about 

 half, and below nearly the whole breadth of every succeeding inner turn ; sur- 

 face unknown ; umbilicus rather small, or about equalling the breadth of the 

 widest part of the outer volution ; aperture nearly obovate, its longer diameter 

 being directed outward and upward. Height, (MO inch ; breadth, 17 inch. 



Named in honor of Dr. John Evans, Geologist, of Oregon. 



Locality and position. Estuary beds at the mouth of Judith River. 



PLANORBrs vetulus, M. & H. Shell discoidal, much compressed, spire slight- 

 ly concave, umbilicus shallow, very little broader than the concavity on the 

 upper side, and rather more than one-third wider than the outer whorl, show- 

 ing about half of each inner turn ; volutions three and a half to four, compress- 

 ed convex above and below, the upper side being a little more convex than the 

 other, and sloping slightly outward from near the inner margin, rather distinct- 

 ly angular around the outer side, a little below the middle, and deeply concave 

 within for the reception of each succeeding inner whorl ; sutures well defined, 

 though not very deep ; aperture sub-cordate, approaching an irregular hastate 

 outline, very slightly oblique, having its longer axis in the direction of the 

 greatest breadth of the shell ; surface apparently nearly smooth, or only show- 

 ing obscure marks of growth. Greatest breadth 23 inch ; height 005 inch. 



Locality and position. Upper part of the Tertiary forming the Bad Lands of 

 White River. 



Planorbis Leidyi, M. k H. Shell small, 3ubdiscoidal ; spire flat, or a little 

 concave ; volutions scarcely three, increasing rather rapidly in size, not embrac- 

 ing on the upper side, inner ones almost entirely hidden by the last turn below, 

 all convex above, rather narrowly rounded on the upper outer side, ventricose 

 and rounded below ; suture will defined ; umbilicus small, or less than half the 

 breadth of the outer whorl, deep and scarcely permitting the inner volutions to 

 be counted; surface marked by fine delicate lines of growth ; aperture sub- 

 circular, or obliquely a little oval, flattened or somewhat concave on the inner 

 side. Greatest breadth, 0-22 inch ; height, 0-09 inch. 



Named in honor of Prof. Jos. Leidy of Philadelphia. 



Locality and position , same as la^t. 



CONCHIFERA. 



Sph^riom planum, M. & H. Shell rather small, broad oval or subcircular, 

 much compressed ; extremities more or less regularly rounded, the posterior mar- 

 gin being sometimes faintly subtruncate ; base semi-oval in outline ; cardinal 

 margin rounding gradually from near the middle ; beaks very small, compressed, 

 and scarcely extending beyond the hinge margin, nearly central ; surface marked 



I860.] 



