DESCRIPTIONS OF NEW SPECIES. 115 



from base to beaks, seven and a half centimeters; greatest breadth, which 

 is near the base, five centimeters; length. of hinge, thirty-seven millimeters. 



This shell somewhat resembles I. fragllls Hall and Meek, but differs 

 from it in possessing the shallow radiating furrow upon the body of the 

 valve, and also in having a distinct posterior ear, separated from the body 

 of the valve by an auricular furrow. It also resembles an example of /. 

 striatus Mantell, in the cabinet of the Smithsonian Institution, from Saxony, 

 but the beaks of our species are more elevated and turned more forward 

 than they are in that species. I. striatus is also without the shallow radiat- 

 ing furrow before mentioned. It differs from I. flaccidus White in its smaller 

 size, its smoother surface and more gibbous valves, that species being coarsely 

 and extravagantly wrinkled. Specific name given in honor of Mr. E. E. 

 Howell, who discovered it while geologist of one of the surveying parties. 



Position and locality. Henry's Fork Group; Lower Potato Valley and 

 Upper Pine Creek, Utah. 



Genus AVIOULA Klein. 



Avicida Parkensis (sp. nov.). Shell small, slightly inequivalve, very 

 oblique, elongate, thin at all the margins except the cardinal; anterior wing 

 of ordinary size and shape; posterior wing rather large arid long; both 

 valves broadly but regularly convex; body of the shell broadest behind the 

 middle; antero-basal border broadly convex; posterior extremity regularly 

 rounded; postero-dorsal border nearly straight from the posterior border to 

 the base of the posterior wing; beaks of ordinary prominence; surface ap- 

 parently smooth. 



Length from the end of the anterior wing to the posterior extremity of 

 the shell, thirty-four millimeters; breadth across the widest part of the body, 

 fifteen millimeters. 



This species resembles A. lingulifera Shumard, but differs from that 

 species in its more elongate form and more oblique hinge line. 



Position and locality, Cretaceous strata; south of Grand River, Middle 

 Park, Colorado. 



Genus ARCA Linna3us. 



Area? Coalvillensis (sp.nov.). Shell longer than high, moderately thick; 

 test somewhat massive; beaks depressed, situated near the anterior end; 



