254 
PALAEONTOLOGY OF NEW-YORK. 
Numerous fragments of articulations of the thorax were found with the specimens 
here figured. In one of these, an articulation of the lateral lobe is marked by a broad 
groove, extending about two-thirds of its length from the axis; beyond which, it presents 
a broad flattened surface, sharpened upon the upper edge, and obtuse at the extremity. 
Fig. 4 a. The caudal shield of a small individual. 
Fig. 4 b. A fragment of the lateral lobe of the caudal shield of a larger individual. 
Position and locality. This species has been seen only in a single fragment of slate, from 
near Watertown, Jefferson county. I should not have ventured to figure it in this place, 
since there is some little doubt as to its precise locality ; but that the same fragment contains 
one or two other peculiar fossils, known only in the slates of this period. 
(From Dr. I. B. Crawe.) 
43. 1. ISOTELUS GIGAS. 
Pl. LXVI. Fig. 5. 
Reference pag. 231, pi. 60, 61, 62 and 63 of this report. 
I have obtained from the Utica slate, in the Mohawk valley, the large labrum here 
figured. The dimensions are twice as great as any other specimen I have seen ; and judging 
from this circumstance, the animal must have been at least eighteen inches long. The 
distance between the extremities of the processes is less, and these parts are proportionally 
shorter than in specimens from the Trenton limestone; but these differences do not appear 
to be sufficient to found specific distinctions. 
Fragments of other portions of this species are often found in this slate, and also in the 
shales of the Hudson-river group; but the animal does not appear to have existed in any 
considerable numbers, after the deposition of the Trenton limestone. 
