198 PALEONTOLOGY OF NEW-YORK. 



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, Lajlarck sp. ( Terebra- 

 tulites ostiolatus, Scinx)THEiM), from wliich it differs in being less gil)bous with a 

 greater number of plications, and in having adcpressed line along the mesial fold 

 of the dorsal valve. It may be easily distinguished from 8. euniteines 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 ago of the Upper Hel- 

 derberg : Falls of the Ohio, Charleston landing and other places. 



Spirifera acuminata. 



PLATE XXIX. 



DeltkyrU acuminata : Conrad, Annual Report of the Palseontology of New York, p. 65. 1839. 

 Spiri/er acuminatus .■ (Conrad,) Hall in Tenth Report ou the Stale Cabinet, p. 135, 1857. 

 Compare Spirifer eultrijugatut, R<emer in DaH RhenischcUebergangsgcbirge, p. 76, pi. !v, f. 4, a, b,c. 1844 

 Also t Spiri/er cultTijugatut : (Rceher) Scnsca Pala;ontographica, Vol. iii, pi. xxiii, f. 1. 



" •' (R(emer) Davidson's Monograph of British Devonian Brachiophoda, p. 86. 



Also DeltkyrU prora : Coskad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, p. 263. 1842. 



" D. ACUMINATA. Shell subcordate, dilated transversely ; valves Avith [radiating 

 " sulci : superior valve very prominent and carinatcd in the middle ; carina 

 " not sulcated, slightly arcuate in length ; lateral extremities rounded ; ba«e 

 " cmargiuatc ; inferior valve profoundly bilobed ; sulci not deeply impressed ; 

 " beak approximate. Length 2^ inches. Locality/ : Ilelderberg, in limestone. 

 " It rc8eml)le8 Atrypa acuminata (Sowerby). 



