508 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Physa Carletoni, Meek. 



Shell iiiombic-snl)ovate, attaining a tnedium size; very tliiii; spire 

 sbort and small; volutious about three, last oue very large, or t'ormiug 

 near nine-tenths the entire bulk of the shell; aperture unknown ; sur- 

 (ace showing rather obscure lines of growth. 

 ' Length, O.oO inch; breadth, O..'}") inch. 



The only specimen of this species I have seen is somewhat imperfect, 

 .and so connected with a portion of the arenaceous matrix that its 

 aperture and columella cannot be seen. It seems to have most nearly 

 resen)bled such recent species as P. Lordi, Baird, in general form. I 

 should not have attempted to name and characterize the species without 

 seeing the columella and aperture, had it not seemed desirable to call 

 attention to it as the tirst species of the genus hitherto found in the 

 well-marked Cretaceous strata of this country. 



The specihc name is given in honor of Mr. Benjamin Carleton, the 

 gentleman who owns the coal-mine at which the specimen was found, 

 and assisted us in collecting the fossils found at the same. 



Locality and position. — Carleton's coal-mine, near Coalville, Utah, in a 

 Cretaceous bed, associated with Unio, Cardinm, Inoccramus, Anomia, 

 Ncritina, and other marine and iresh-water shells. 



Species from the Bitter CreeTc series. 

 OsTREA Wyomingensis, Meek. 



Oslrea Idrhieusis ? ? Meek, 1S72. Hayden's Geological Report, Montana, &c., p. 375, 



(not 0. Idriaensis, Gabb.) 



Oslrea Wyomingcnsis, Meek, 1S72; ib. 



Shell attaining a moderately large size, rather compressed, subovate, 

 or trigonal-subovate, being i)ointed at the beaks, and more or less 

 rounded at the opposite extremity. Lower valve usually rather shallow ; 

 beak generally somewhat acutely pointed, undistorted, and nearly al- 

 ways curved upward at the extremity; ligament area comparatively 

 small, trigonal, with the longitudinal furrow and transverse stritie well 

 defined ; posterior lateral margins flattened, and rather broad, in conse- 

 quence of the lateral expansion of the imbricating laminas of growth j 

 muscular scar comparatively small ; surface with only irregular imbri- 

 cating but not strongly projecting laminte of growth. Ui)per valve 

 smaller than the other, nearly flat on the upper side and slightly con- 

 cave within ; beak less pointed than in the other valve, being usually a 

 little truncated at the extremity, which is straight or nearly so ; liga- 

 ment area of the same size and nearly the same form as in the other 

 valve, excepting that it is not curved, but directed obliquely upward 

 and backward, find has its anterior margin forming a transverse ridge, 

 as usual most prominent in the middle at the end of the mesial longi- 

 tudinal ridge, which is rounded, or somewhat flattened, and continued 

 'to the point of the beak; posterior lateral margins thickened in adult 

 shells, and only rarely showing slight traces of creuulations; surface as 

 in the other valve. 



Length of large examples from beak to anterior extremity, inches; 

 breadth, 4 inches. .Average-sized specimens are generally a little nar- 

 rower in proportion to length. 



In Dr. Ilayden's report of 1872, I referred this oyster with much 

 doubt to 0. Idriaensis, Gabb; but at the same time expressed the opin- 

 ion that it would probably i)rove to be a distinct and undescribed species, 



