LOWER SILURIAN OR CAMBRO-SILURIAN AGRE.


form give rise to the popular impression that they are fossilized ser-
pents. When split longitudinally, as they not unfrequently are by
the fracturing of the rock, the siphuncle and septa give an appear-
ance resembling the backbone and ribs of a vertebrate, seemingly
confirming the impression that they are snakes or fishes, forms only
found in much later ages. Upwards of thirty species of Trenton
Cephalopods occur in the State, of which the following may be
mentioned as representative:  Orthoceraajunceum, 0. multicamera-
FIG. 35.


TRENTON CEPHALOPODS. a. Endoceras subannulatum - Whitf. b. Fragment of same
show.
ing siphuncle. c. Gyroceras duplicostatum - Whitf. d. Oncoceras brevicurvatum
- Hall.
e. 0. Pandion - Hall. f. 0. Mumiaformis -Whitf. g. Fragment of Orthoceras
Beloitense -Whitf.
h. Cyrtoceras planodorsatum -Whitf.


turn, Actinoceras (Orthoceras) Beoitense, Ormoceras tenuifluam,
Endoceras annulatum, Gonioceras anceps, and Lituites occidentals.
The giant forms of this class were doubtless masters of the seas, and
preyed upon such inferior animals as were not agile enough to escape
them, or were unprotected by shells or other defenses.
Annelids. The calcareous bottom of the ocean was apparently
uncongenial to the sand-boring Annelid8, but occasional worm-like
tubes imply at least their limited existence.
Crustaceans. Among the Crustaceans, there were large numbers
of the little Entomostracans, Leperditiafabulites, which protected its


1019




Z




I!