88 PALEONTOLOGY. 



panied by some other differences, it would be unsafe to view our shell as 

 belonging to a distinct species ; though it is barely jDOSsible that it may 

 prove to be such. One of the specimens shows that it has the transverse 

 septum and the split tube between the dental laminsB, now known to exist 

 in S. cuspidatus. I have not been able yet to see evidences of the shell 

 being punctate, though I have not given it a thorough examination, and 

 believe that it will be found to possess that character also. 



Locality and position.—WhitQ Pine Mountains, Treasure Hill, Nevada ; 

 .exact position not known, but it is believed to have come from a gi'ay semi- 

 crystalline limestone holding a position between well-marked Carboniferous 

 and Devonian rocks, and probably belonging to the former epoch. 



Spiripee (Trigonotreta) opimus, Hall ?. 



Plate 9, fig.*6. 



Spirifer opimus, Hall (1858), Geol. Eeportof Iowa, I, part ii, 711, pi. xxviii, figs. 1 a, &, 

 Spirifer subventricosus, McCbesney (1860), Descriptious New Palaeozoic Fossils, etc., 44; 



and Trans. Chicago Acad., I, pi. i, fig. 4. 

 Compare Spirifer Msulcatus, Sowerby (1825), Mio. Conch., V, 152, pi. 494, figs. 1 and 2; 

 also ;S'. Rocky montana, Marcou (1858), N. Am. Geol., 50, pi. vii, figs. 4, 4 a-e ; 

 8, KeoTculc, Hall, var. (1858), I«wa Eeport, I, pi. xx, and pi. xxv, and 8. incre- 

 bescens, Hall, lb., pi. xxvii, figs. 6 a-i ; also 8. KeokuJi, var. Shelbyensis, Swal- 

 low (1867), Trans. St. Louis Acad., If. 



Shell attaining nearly a medium size, moderately gibbous, subequi- 

 valve ; hinge about equaling the greatest breadth ; lateral extremities sub- 

 rectangular, slightly rounded, or more or less than rectangular; front having 

 a general subsemicircular outhne, sometimes a little projecting in the middle. 

 Ventral valve most convex in the umbonal region ; beak rather pointed and 

 distinctly incurved ; area of moderate height, strongly striated vertically, 

 and arched with the beak ; mesial sinus narrow, rather shallow, and nar- 

 rowing gradually to the apex of the beak, occupied by generally four 

 costae, a little smaller than those on each side, with which the lateral ones 

 usually coalesce before reaching the umbo ; lateral slopes each occupied by 

 from eleven to thirteen, most generally simple, but sometimes in part bifur- 

 cating costae, crossed on well-preserved specimens by moderately distinct, 

 undulating marks of growth. Dorsal valve most convex near the middle ; 

 beak strongly incurved; mesial fold corresponding in size and form with 



