I90 PALAEONTOLOGY OF NEW-YOUK. 



median crest. A cast of the dorsal valve shows rather shallow teeth- 

 sockets, with a strong callosity between them and the fissure, while the 

 apex is marked by muscular impressions. 



This species ha.s ordinarily Ji width on th(> hin£»e-linc of :in ineh to an inch 

 and a quarter, sometimes reaciiing an incli an 1 a half; with a length of a1)out 

 three-fourths of an inch, and rarely of larger dimensions. It presents little variety 

 of form aud proportions ; the younger individuals observed having three or four 

 ribs on each side of the mesial fold and sinus. The cardinal extremities are rarely 

 more extended than in the specimen figured. 



In many of its features this .species resembles the S. ci/cloptera of the Lower 

 Helderberg group, but it is usually more extended on the hinge-line, with narrower 

 area and less conspicuous surface stria?. In casts of the dorsal valve, however, the 

 two are scarcely distinguishal)le. It is of the type of >S. speciosa of Sciilotheim, 

 with a narrower area and more ribs than the Eifel specimens, but corresponding 

 in tliis respect to the I^nglish Devonian specimens iigured by Mr. Davidson. 



Geological formations and localities. Tliis species begins its existence, so far 

 as at present known, in the Schoharie grit, in which it is common in the form of 

 casts throughout the eastern part of the State. In the Cornifcroiis limestone, it is 

 known through all the extent of the formation within the State, and occurs in 

 Canada West, and in Ohio, It is unknown to me in the Hamilton group. 



Spii'ifera macia. 



PLATE XXVII. 



Spirifer macra : Hall, Tenth Report on the State Cabinet, p. 134. 1857. 

 " •' New Species of Palaeoroic FossiU, p. 94. 1857. 



Seiell transverse, semielliptical, semicircular or subtriangular ; hinge- 

 line equalling or greater than the width of the shell beloAv, the cardi- 

 nal extremities produced into mucronate extensions : valves unequally 

 convex. 



Ventral valve more convex than the dorsal, gibbous above the middle, 

 sometimes regularly Qonvex or arcuate, but often less convex on the 

 lower half; compressed towards the cardinal extremities : mesial 

 sinus of moderate width, shallow, but sharply defined at the margins ; 

 beak much elevated and slightly incurved over the large fissure ; area 

 high, triangular, concave. 



