110 INVERTEBltATE PALEONTOLOGY. [WHITE. 



JURASSIC PERIOD. 



Mollusca. 



Conchifera. 



Genus UNIO Retzius. 



Unio Stewardi (sp. nov.). From the Jurassic strata at Flaming Gorge 

 of Green River, near the northern boundary line of Utah, some portions of 

 a moderately large Unio were obtained that belong to an undescribed 

 species. The valves are broadly oval in marginal outline, broadly but 

 somewhat uniformly convex ; beaks very near the anterior end ; test 

 massive ; surface apparently marked only by the ordinary lines and imbri- 

 cations of growth ; cardinal and lateral teeth both strong ; the lower lateral 

 tooth of the left valve, and also that part of the hinge of the right valve 

 against which it shuts, both strong and rounded into the cavity of each 

 valve respectively, and both ^nd posteriorly by abruptly rounded ends. 



Length of largest example, eight and. a half centimeters ; height, sixty- 

 two millimeters. 



Compared with U. nucalis Meek and Hayden, the only other species 

 of the genus known to me from American Jurassic strata, it is larger, more 

 massive, the beaks placed more anteriorly, and the cardinal and lateral 

 teeth more massive. 



Specific name given in honor of Mr. J. F. Steward, of Piano, 111., its 

 discoverer. 



Gasteropoda. 



Genus NERITINA Lamarck. 



Neritini ? ? Powelli (sp. nov.). Shell moderately large, obliquely sub- 

 ovate in outline ; volutions about three or three and a half, rapidly increas- 

 ing in size, the last one much expanded ; spire depressed, the apex scarcely 

 appearing by side view of the shell ; suture slightly impressed ; aperture 

 large, broadly subcircular or subtetrahedral ; a broad rounded revolving 

 prominence extends around the volutions, nearer to their distal than prox- 

 imal side, and another less prominent one between the first one and the 

 suture ; the first one, especially, gives a degree of angularity to the last 

 volution and to the margin of the aperture. 



