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PALAEONTOLOGY OP NEW-YORK. 
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 has ordinarily a width on the hinge-line of an inch to an inch 
and a quarter, sometimes reaching an inch and a half; with a length of about 
three-fourths of an inch, and rarely of larger dimensions. It presents little variety 
of form and 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 8. cycloptera of the Lower 
Helderberg group, but it is usually more extended on the hinge-line, with narrower 
area and less conspicuous surface strife. In casts of the dorsal valve, however, the 
two are scarcely distinguishable. It is of the type of 8. sjpeciosa of Schlotheim, 
with a narrower area and more ribs than the Eif'el specimens, but corresponding- 
in this respect to the English Devonian specimens figured by Mr. Davidson. 
Geological formations and localities. This 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 Corniferous 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. 
Spiiifera macra. 
PLATE XXVII. 
Spirifer macro.: Hall, Tenth Report on the State Cabinet, p. 134. 1857. 
“ u New Species of Palaeozoic Fossils, p. 94. 1857. 
Shell transverse, semielliptical, semicircular or subtriangular; hinge¬ 
line equalling or greater than the width of the shell below, the cardi¬ 
nal extremities produced into mucronate extensions : valves unequally 
convex. 
Ventral valve more convex than the dorsal, gibbous, above the middle, 
sometimes regularly convex 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. 
