58 
PALEONTOLOGY OF NEW YORK, 
Distribution. Upper Helderberg group. Corniferous limestone; in the decom¬ 
posed chert boulders, Canandaigua, Ontario county. 
Dalmanites (Corycephalus) dentatus. 
PLATE XI A, FIGS. 4-6. 
Dalmanites dentata, Barrett. Amer. Jour. Science, voL xi, 3d Ser., p. 200, plate. 1876. 
Dalmanites dentata, Barrett. Amer. Jour. Science, vol. xii, 3d Ser., p. 70. 1876. 
This interesting Lower Helderberg species is the earliest known form of Dal¬ 
manites which presents a development of the ornamentation of the frontal border 
of the cephalon, a feature which becomes so characteristic of many species of 
this genus in the Upper Helderberg. This ornamentation consists of a single 
row of acute denticulations, about thirty-five in number, decreasing in size 
toward the genal extremities, and in their shape indicating the inception of the 
broader, incisor-like processes of Dalmanites regalis, D. pygmceus and the group 
represented by D. selenurus. In other respects however Dalmanites dentatus 
retains the distinctive characters of the Silurian representatives of this genus, 
that is, forms following the type of Dalmanites Hausmanni, Brongniart, and in 
respect to features, which are not of an ornamental character, is in harmony 
with its associates in the Lower Helderberg formations, viz., D. nasutus, D. tridens, 
D. pleuroptyx. The distinct lobation of the glabella, and the absence of any 
tendency in the first and second lateral lobes to coalesce, the frontal glabellar 
depression, the long, terete thoracic segments, and the narrow, triangular, cau¬ 
date pygidium, are all features, which in their entirety, give a pre-Devonian 
aspect to the species. With the opening of the Devonian age some or all of 
these features appear with modifications so distinct as to require the recogni¬ 
tion of sub-divisions in the genus. A notice of Dalmanites dentatus is introduced 
in this place for purposes of comparison with the Upper Helderberg species, 
and on account of its frontal ornament is referred with D. regalis and D. pygmceus 
to the group, Corycephalus. 
Distribution. Lower Helderberg group. In the shaly limestone at Port Jer¬ 
vis, Orange county; Becraft’s Mountain, near Hudson, Columbia county. 
