20 



equal to or slightly greater than the breadth; antero-lateral and 

 front margins somewhat regularly rounded, the front being slightly 

 straightened, or a little emarginate ; postero-lateral margins converg- 

 ing to the beaks at an obtuse angle. 



Dorsal valve broadly convex from side to side ; convexity from beak 

 to front regular, but a little greater than the transverse ; umbo promi- 

 nent ; beak strongly incurved ; mesial fold obsolete or entirely wanting. 



Ventral valve strongly and somewhat regularly arching from beak to 

 front; convexity from side to side a little less than the longitudinal, 

 and about equal to the transverse convexity of the other valve ; beak 

 somewhat prominent and incurved over the beak of the dorsal valve ; 

 mesial sinus obsolete or wanting. 



Surface marked by a few obscure, radiating striae, which are most 

 conspicuous near the median line of each valve. Fine, concentric striae 

 are numerous ; and in adult shells there are also stoug imbricating lines 

 of growth near the front and lateral margins. 



Length, fifteen millimeters ; width, fourteen millimeters ; height, 

 twelve millimeters. 



This shell has a different aspect from any other species of Eliynclio- 

 nella in the Carboniferous rocks, and some doubts are felt as to its 

 proper reference to that genus ; but the broken ventral beak shows no 

 other characters than those of Rhynchonella, and the shell-structure is 

 not punctate but distinctly fibrous. 



Position and locality. Carboniferous rocks, Kock Canon, Wahsatch 

 range near Provo, Utah. 



RHYIXCHONELLA METALLICA (sp. nov.) Shell rather small, depressed, 

 or moderately inflated when adult, transversely suboval in outline ; antero- 

 lateral borders abruptly rounded ; front broadly rounded and scarcely 

 emarginated; postero-laterai margins straightened, laterally compressed, 

 and meeting the beaks at a very obtuse angle. 



Dorsal valve more capacious than the ventral, broadly convex from 

 side to side, a little flattened near the beak, abruptly bent downward 

 at the margins ; mesial fold broad, not much elevated, discernible only 

 on the anterior part of the valve. 



Ventral valve comparatively shallow, slightly convex from side to 

 side, and the same also from the urnbo to the antero-lateral margins; 

 beak small, prominent, and incurved over that of the dorsal valve ; 

 mesial sinus broad, becoming obsolete near the middle of the shell. 



Surface marked by from fourteen to sixteen simple angular plica- 

 tions upon each valve, with angular interspaces of similar width between 

 them, all of which are continuous to the beaks ; about four of these are 

 borne in the mesial sinus, and five upon the mesial fold. 



Length, ten millimeters; breadth, twelve millimeters; height, seven 

 millimeters. 



This species resembles R. Cooperensis Shutnard from the Subearbon- 

 iferous strata of Missouri, but differs in having a less number of plica- 

 tions, and in wanting the numerous filiform, radiating striae of that 

 shell. 



Position and locality. Strata of the Carboniferous period, Old Potosi 

 mine, Lincoln County, Nevada. 



Genus SPIRIFER Sowerby. 



SPIRTFER (MARTINIA) GLABER var. CONTRACT A Meek and Worthen. 

 The collection contains specimens from Camp Cottonwood, Lincoln 

 County, Nevada, that I am unable to separate from the above-named 



