CARBONIFEROUS PERIOD. . 109 



ence between our species and P. hiarmica, and has also given for comparison 

 a copy of Count Keyserling's figure, together with a copy of tire figure of 

 the species given by Dr. Geinitz. 



Position and locality. — Strata of the Carboniferous period at the con- 

 fluence of White Mountain and Black Rivers, Arizona. 



Class BRACHIOPODA. 



Order ARTHROPOMATA. 

 Family PEODUCTIDiE. 



Genus PRODUCTUS Sowerby, 1812. 



Productus costatus Sowerby (?). 



Plate VIII, fig. 2 a, h, c, and d. 



? Producta costata Sowerby, 1827, Min. Conch., vi, 115. 



? Producta costellata McCoy, 1844, Synop. Carb. Foss. of Ireland, 108. 



? Productus costatus de Verneuil, 1845, Geol. Russ. et. Ural Mis., ii, 268. 



? Productus costatus de Kouinck, 1847, Monog. Product., pi. viii, f. 3, and pi. x, f. 3. 



Productus Portloclcianas Norwood and Pratteu, 1854, Jour. Acad. Nat. Sci. Phila., viii, 15. 



Prodtictus costatus Shnmard, 1855, Geological Report Missouri, 216. 



Productus costatus var. Hall, 1858, Geology of Iowa, i, pt. 2, 712. 



? Prodtictus costatus Davidson, 1860, Monog. British Garb. Brachiopoda, 153. 



f Productus viminalis White, 1862, Proc. See. Nat. Hist. Boston, ix, 29. 



Productus costatus ? ? Meek, 1872, U. S. Geol. Sarv. Nebraska, 159. 



Shell of medium size ; width greater than the length, measured in a 

 straight line from hinge to front border, strongly and deeply arcuate ; 

 hinge-line nearly or quite equal in length to the greatest width of the shell ; 

 ears thin, well defined, and bent slightly downward ; free margin broadly 

 rounded, front emarginate. 



Ventral valve very gibbous and strongly curved, having a broad 

 shallow sinus extending from the umbonal region to the front, producing 

 there the before-mentioned emargination of the front border ; beak promi- 

 nent, incurved, but only very slightly projecting over the hinge-line. 



Dorsal valve flattened or only slightly concave in the visceral region, 

 abruptly curved upward at the lateral and front margins ; front showing a 

 very slight mesial fold, corresponding with the broad, shallow mesial sinus 

 of the other valve. 



