20 



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

 front margins somewhat regularly rounded, the front being slightly 

 straightened, or a little emarginate ; posterolateral 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 strife, which are most 

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

 are numerous; and in adult sbells there are also stong 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 Rhyncho- 

 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, Eock Canon, Wahsatch 

 range near Provo, Utah. 



Rhynchonella 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 ; posterolateral 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, slightl3^ convex from side to 

 side, and the same also from the umbo to the anterolateral 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 siuiilar 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, sev^en 

 millinieters. 



This species resembles R. Cooperemis Shumard from the Subcarbon- 

 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 speciuiens from Camp Cottonwood, Lincoln 

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



