292 
PALAEONTOLOGY OF NEW YORK. 
tures, but the septa are a little more frequent, and none of the specimens 
referred to that species have shown any indication of the ventral carina on the 
cast of the interior. 
Formation and locality. In the shales of the Hamilton group at Monteith’s 
Point, Canandaigua lake, N. Y. 
Orthoceras emaceratum. 
PLATES XXXIX, FIG. 4 ; LXXXV, FIG. 16. 
Orthoceras emaceratum. Hall. Fifteenth Rep. N. A 7 . State Cab. Nat. Hist., p. 170, pi. 8, fig’. 7. 1862. 
“ “ “ Illustrations of Devonian Fossils: Cephalopoda. Explanation of plate 39, 
fig. 4. 1876. 
Shell straight, slender, gradually enlarging from the apex. Transverse section 
subcircular. Apical angle 4|°. Initial point unknown. 
Chamber of habitation not observed. Air-chambers regular, gradually 
increasing in depth toward the grand chamber, varying from six to nine mm. 
in the length of eighty mm. 
Septa and siphuncle unknown. Sutures straight and horizontal. 
The test has not been preserved, but some specimens show traces of trans¬ 
verse striae. 
The internal mould is smooth, with the sutures but little impressed. 
One fragment, embracing twenty air-chambers, has a length of 125 mm., 
with a diameter at the smaller extremity of ten mm. Another portion of a 
larger individual has twelve chambers in the length of ninety mm. 
All the specimens of this species are from the soft shales in the western part 
of the State. They are usually much flattened and broken from compression, 
and the test has been destroyed. The distinguishing characters are the depth 
of the chambers, compared with the diameter of the tube, and the small apical 
angle. In its general aspect and association it is similar to 0. aulax; but the 
marked surface ornaments on the latter species, which are also shown on the 
internal mould, are characteristic. 
Formation and locality. In the soft shales of the Hamilton group, in Genesee 
and Erie counties, N. Y. 
