CEETACEOUS FOSSILS. 167 



surface-markings or other characters. My present opinion, hoAvever, is, that 

 it may find a place in some of the previously-proposed sections of Unto. 



Locality and position. — The typical specimens of this species were 

 brought by Dr. Hayden from Limestone Hill, on Bear River, Utah. Mr. 

 King also found it on the same river, beneath indications of lignite. Speci- 

 mens were also sent by Mr. H. R. Durkee to the Smithsonian Institution, 

 from the same horizon at Gilmer, Wyoming. 



CYRENID-^. 



Genus CORBICULA, Benson. 

 CoRBicuLA (Vbloritina) Duekeei,- Meek. 



Plate 16, figs. 6, a, h, c, d, e,f, g. 



Cyrena {Corbicula?) Durkeei, Meek (1870), Proceed. Acad. ISIat. Sci. Philad., XI, 431. 

 Corbicula (Veloritina) DurTieei, Meek (1872), Hayden's Second Ann. Eeport U. S. Geol. 



Survey of the Territories, 294. 

 Cyrena {Yeloritina) Durlieei., White (187G). Eeport on Lieut. Wheeler's collections, 207, 



pi. xxi, fig. 13. 



Shell attaining a large size, thick, trigonoid-subcordate, gibbous, oblique, 

 with length exceeding somewhat the height, most convex a little in advance 

 of and above the middle, and cuneate postero-ventrally ; posterior dorsal 

 slope long, straight, or slightly convex in outline from the umbones to the 

 angular or subangular posterior basal extremity; basal margin semi-ovate in 

 outline, being most prominent anteriorly ; anterior margin short, descending 

 very abruptly from the beaks, with a slightly concave outline above, and 

 rounding regularly into the base below; beaks elevated, gibbous, obliquely 

 incurved, contiguous, and placed about half-way between the middle and 

 the anterior end, or sometimes nearly over the latter; posterior umbonal 

 slopes prominently rounded, with posterior dorsal margins inflected or 

 incurved so as to form a profound, broad concavity, or sulcus, along their 

 entire length, as the two valves are seen united; lunule in most cases deep, 

 but generally without Avell-defined margins; ligament short, narrow, and so 

 deepLy seated in the broad dorsal concavity as not to be visible in a side- 

 view when the valves are united; surface only showing moderately distinct 

 lines of growth; hinge strong; cardinal teeth oblique, excepting the anterior 



