BIRDSEYE LIMESTONE. 
227 
TRILOBITES OF THE BIRDSEYE LIMESTONE. 
Plate LX. ( in part ). 
291. 1. OGYGIA? VETUSTA. 
Pl. LX. Fig. 1. 
Compare Asaphus tyrannies, Murchison, Sil. System, pi. 24, and pi. 25, fig. 1 a, b. 
Caudal shield obtusely subtriangular; middle lobe with 16 articulations, abruptly nar¬ 
rowing from above towards the middle, below which it is of nearly equal width ; lateral 
lobes with 15 distinct segments, the posterior ones meeting the middle lobe at a very acute 
angle, and terminating in a thickened or recurved border ; surface, near the margin, 
marked by imbricating lines or lamellose striae. 
The only specimen yet known is the caudal shield here figured ; it bears a very close 
resemblance to the A. tyrannus of Murchison, and, from its geological position, it is doubt¬ 
less a closely allied species. It will at once be recognized by the numerous segments of the 
caudal shield, the axis of which reaches only about -f- of the whole length. A few of the 
last articulations of the lateral lobes are nearly parallel to the central lobe, while the first 
ones are nearly perpendicular to it. Each articulation of the lateral lobe is marked by a 
sudden and slight bending or contraction, about two thirds the distance from the axis to 
their outer extremity. The specimen is almost denuded of the crust, so that its original 
character cannot be entirely known. 
I have referred this species to the Genus Ogygia, on account of the striated or lamellose 
surface, which does not belong to any of the species of Piiacops with which I am ac¬ 
quainted. In the absence of other portions of the fossil, this reference must be given with 
some hesitation. The surface markings of some species of Asaphus do not differ materially 
from this specimen, and it may prove to belong to that genus. In the present state of our 
knowledge, we must regard the Asaphus and Ogygia as confined to the older silurian 
strata, appearing among the earlier forms of the Crustaceans, and limited to a single epoch 
of geological time. 
Position and locality. In the compact Birdseye limestone of the Mohawk valley. 
29 
