72 rAL.150NTOLOGY. 



i-egarding tliem as belonging' to a distinct species from that form also. Until 

 we can have an oppoilunity to arrive at a more satisfactory conclusion on 

 these points from the study of more extensive collections, I would therefore 

 refer this form provisionally to P. costatus, but at the same time express the 

 belief that it does not belong to the same species as the typical P. costatus 

 of the Old World. 



Locality and position. — Railroad Canon, Diamond Mountains ; Fossil 

 Hill, White Pine Mountain; and Moleen Peak, Nevada. 



Productus Pkattenianus, Norwood. 



Plate 7, liK- 7. 



Productus com, Owen (1852), Geol. Eeport Wisconsin, Iowa, and Jliim., 103 and 130, 



pi. V, fig. 1.— Marcou (1858), Geol. N. Am., 4.'5, pi. vii, fis^s. 4, 4 a. 

 Productus semiretlculatus, Hall ^1852), Stausbury's lieport Salt Lake Exp., 411, pi. 



iii, figs. 3, 5, and 5rt, b (not Martin, sp.). 

 Productus Prattenianus, 'Horwood (1854), Jour. Acad. Nat. Sci. PUilad. (2d ser.). Ill, 



p. 17, pi. 1, figs. 10 a, ft, <•, d. 

 Prodtictus Flemingii, Geinitz (1800), Carbonf. und Dyas in Nebraska, 52, taf. iv, figs. 



1. 2, 3 (not Sowerby). 

 Compare P. cora, d'Orbigny (1843), Paleont. Voy. Am. Merid., Ill, 55, pi. v, figs. 8, 'J. 



This is a common shell in the Coal-Measui-es of the Mississippi Valley, 

 through the whole thickness of which it ranges, if not into the Lower Car- 

 boniferous. It is generally about as wide as long, by direct measurement 

 from beak to front ; though in some examples the anteiior margin is more 

 produced. The hinge-line, usually equals the greatest breadth ; while the 

 ears are large, rectangular, and marked with a few large wrinkles that extend 

 a little upon the sides of the umbo, but never cross over it, the visceral 

 region of the ventral valve being nearly always without traces of these 

 wrinkles. It is very gibbous, strongly-arched in the umljonal region, and 

 without any indications of a mesial sinus, though it is sometimes a little flat- 

 tened in the middle, Avith the lateral slopes rounding down abniptly on each 

 side. The beak is often narrow^ed and distinctly incurved. The surface is 

 ornamented by fine, regular, longitudinal stria?, which increase by intercala- 

 tion, or sometimes by division; while over the whole of the ventral valve 

 are distantly, but regidarly scattered, a few large spine-bases, at each of 

 which the strife are often interrupted, sometimes three or four of them termi- 



