250 
PALAEONTOLOGY OF NEW-YORK. 
TRILOBITES OF THE UTICA SLATE AND HUDSON-RIVER GROUP. 
Plate LXVI. ( in part ). 
The important and characteristic Trilobites of these rocks are species which appear, 
though less conspicuously, in the Trenton limestone, and have been already noticed. The 
rule I have adopted, however, renders it necessary to speak of them here, giving illustra¬ 
tions of specimens from these rocks. The most numerous forms are those of Calymene 
beckii and Trinucleus concentricus ; and the condition of the specimens in the slialy strata is 
so different from the same in the compact limestone, that both require illustration. Two or 
three forms appear in these rocks, which are thus far unknown in the limestones below, 
and which are probably peculiar to this period, becoming developed only after the com¬ 
mencement of argillaceous deposits. 
297. 2. CALYMENE BECKII. 
Pl. LXVI. Figs. 2 a-k; and Pl. LXVII. Figs. 4 a, b, c, d, e. 
Reference pag. 237, pl. 64 of this report. 
Much confusion has arisen respecting this species, which is abundant in the Utica slate. 
It was first described by Prof. Eaton, under the name Brongniartia , from imperfect 
specimens of the cephalic shield, in the calcareous beds of the Utica slate, at Coldspring, 
Montgomery county. These specimens are more convex than those in the softer slate, and 
their true character is not obvious on a cursory examination. Prof. Green substituted the 
name of Triarthrus for that proposed by Prof. Eaton ; still regarding the small imperfect 
cephalic shields as the entire animal. Dr. Harlan, in correcting this error of Eaton and 
Green, described the buckler as destitute of oculiform tubercles; and I have, myself, 
fallen into the same error in describing as distinct species two nearly entire specimens, 
owing to the absence of the maxillary shields in one, and their partial preservation in the 
other.* 
Silliman’s Am. Jour. Science, Vol. xxxiii, p. 137. 
