PALAEONTOLOGY OP NEW-YORK. 
198 
partially enclose an oval muscular area, which in its upper part is divi¬ 
ded by a short prominent median crest. In some silicified specimens, the 
conical spires are partially preserved. The crura are widely separated at 
their bases, and, converging somewhat abruptly, curve into the dorsal 
valve, making twelve or more turns, and producing a short strong spire. 
In well preserved specimens, the mesial fold and sinus are usually 
sharply defined; but in some of the more gibbous forms, the sinus is 
very broad, and one or two. of the plications on each side are involved 
in the sides of the depression : at the same time the mesial fold is very 
prominent, rounded, and sloping almost imperceptibly into the general 
contour of the convexity of the valve. 
This species is abundant in the neighborhood of Louisville and other western 
localities. It has generally been referred to S. Icevicosta , Lamarck sp. ( Terebra - 
tulites ostiolatus , Sciilotheim), from which it differs in being less gibbous with a 
greater number of plications, and in having a depressed line along the mesial fold 
of the dorsal valve. It may be easily distinguished from S. euruteines of Owen, 
with which it is associated, by its narrower and much more arcuate area and less 
angular plications. Some specimens show remains of a faint impressed line along 
the centre of each plication. 
Geological formations and localities. Limestone of the age of the Upper Hel- 
derberg : Falls of the Ohio, Charleston landing and other places. 
Spirifera acuminata. 
PLATE XXIX. 
Delthyris acuminata : Conrad, Annual Report of the Palaeontology of New York, p. 65., 1839. 
Spirifer acuminutus .• (Conrad,) Hall in Tenth Report on the State Cabinet, p. 135, 1857. 
Compare Spirifer cultrijvgatus, R<emer in Das Rhenische Uebergangsgebirge, p. 76. pi. iv, f. 4, a, b,c. 1844 
Also ? Spirifer cultrijvgatus : (RceSier) Schnur Palseontographica, Vol. iii, pi. xxiii, f. 1. 
“ (Rcemer) Davidson’s Monograph of British Devonian Brachiophoda, p. 35. 
Also Delthyris prora : Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, p. 263. 1842. 
“ D. acuminata. Shell subcordate, dilated transversely; valves with [radiating 
“ sulci : superior valve very prominent and carinated in the middle ; carina 
“ not sulcated, slightly arcuate in length; lateral extremities rounded; base 
“ emarginate ; inferior valve profoundly bilobed ; sulci not deeply impressed ; 
“ beak approximate. Length 2\ inches. Locality : Helderberg, in limestone. 
“ It resembles Atrypa acuminata (Sowerby). 
