BIRDSEYE LIMESTONE. 



227 



TRILOBITES OF THE BIRDSEYE LIMESTONE. 



Plate LX. ( in part ). 

 291. 1. OGYGIA? VETUSTA. 



I'L. LX. Fig. 1. 

 Compare Jlsaphus tyrannus, Murchison, Sil. System, pi. 21, and pi. 2.'), fig. 1 a, i. 



Caudal shield obtusely subtriangular ; middle lobe with 16 articulations, abruptly nar- 

 rowing from above towards the middle, below which it is of nearly equal wichb ; 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 striee. 



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 ^ of the whole length. A few of the 

 last articulations of the lateral lobes are nearly parallel to the central lobe, wiiile the first 

 ones are nearly perpendicular to it. Each articulation of the lateral lobe is marked b}' 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 (he striated or lamellose 

 surface, which does not belong to any of the species of Phacops witii wiiich I am ac- 

 quainted. In the absence of other portions of the fossil, this reference must lie given with 

 some hesitation. The surface markings of some species of Asapitus do not difler 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 2;eolo2:ical time. 



Position and locality. In the compact Birdseye limestone of the Mohawk valley. 



29' 



