nEVONIAN SPECIES. 45 



locality in Neviula, at latitude 39° ,".2' N., longitude 115° 36' W.; Colonel 

 Simpson's (•ollectioii. 



Spirifer (Trigonotreta) PiSonensis, Meek. 



Plate 1, figs. 9, Ho, 9*. 



Spirifer (Trigonotreta) Piiionensis, Meek (1870), Proceed. Acad. Nat. Sci. Philatl., 60. 



Shell attaining about a medium size, somewhat wider than long, vary- 

 ing from transversely-suboval to a nearly semicircular general outline, 

 rather gibbous in adult examples ; cardinal margin nearly or quite equaling 

 the greatest breadth, and terminating in rectangular or rather more obtuse 

 extremities; lateral margins rounding to the front, which is sometimes 

 rounded, sometimes slightly sinuous, or in other examples more prominent 

 and subangiilar in the middle. Ventral valve generally rather more gib- 

 bous than the other, its greatest convexity l)e-ng in the umbonal region, 

 from which it rounds off evenly toward the front and lateral margins as 

 well as to the beak, which projects beyond that of the other valve, and is 

 rather distinctly incurved; cardinal area of moderate height, narrowed to 

 the lateral extremities, more or less inclined backward, and strongly arched 

 with the bsak; foramen having nearly the form of an equilateral triangle, and 

 provided with slightly-raised, sharp, lateral margins; mesial sinus shallow, 

 rounded, smooth, and of moderate breadth, narrowed regularly, and well 

 defined to the apex of the beak. Dorsal valve generally more than semi- 

 circular, most convex in the central and anterior regions ; beak projecting 

 little beyond the cardinal margin, and with the narrow area incurved; mesial 

 ridge depressed, smooth, and faintly fun-owed along the middle, correspond- 

 ing in outline to the form of the sinus in the other valve. Surface of each 

 valve ornamented by from eleven to about fourteen simple, regular, 

 rounded, radiating plications on each side of the mesial fold and sinus, and 

 also showing, under a magnifier, minute, regular, crowded, radiating striiB, 

 crossed near the front by stronger undulating lines of growth. 



Length of a medium-sized specimen, 0.92 inch; breadth of the same, 

 1.20 inches; convexity, 0.72 inch. 



This species seems to be more nearly related to S. Oweni, Hall, from the 

 Upper Helderberg rocks at the Falls of the Ohio, than to any other known 



