354 
PALAEONTOLOGY OF NEW-YORK. 
taceans. The other consists of a median groove or depression marked on each side by a 
double series of imprints, the one a little within the other, as if made by some quadru¬ 
pedal animal : each series of these impressions, however, present an appearance as if 
made by a double claw or foot, rather than by a single one. In general character they 
are very similar to those in the Potsdam sandstone, which have been referred by Prof. 
Owen to a chelonian. The continuous uninterrupted impression of the trail, however, is 
quite unlike the markings made by existing animals of this character ; and yet it is 
evident that the limbs, or appendages making the imprints, extended to some distance 
from the body, and were strong enough to be capable of partially supporting it, leaving an 
undisturbed space between the imprints and the median groove. We infer, therefore, that 
such a track could not have been made by an annelid of the ordinary character. At the 
same time, the imprints do not present any character from which we can infer with 
probability that they were made by any vertebrate quadrupedal animal. 
Upon the same slab with the imprints just alluded to, are others somewhat similar to 
those on Plates xv and xvi of this volume. 
After farther examination of the tracks illustrated on Plates xv and xvi, and a com¬ 
parison with other specimens of a similar character, I am disposed to refer their origin 
to crustaceans rather than to any vertebrate animal. It is impossible, however, to know, 
at the present time, their true origin, and any speculative opinions regarding them must 
be received with caution. 
NOTE B. 
CORALS OF THE CLINTON AND NIAGARA GROUPS. 
Since this volume has been printed, I have seen the work of Milne-Edwards and 
Jules Haime upon the fossil corals of the palseozoic formations*, but too late to give 
any satisfactory notice of its contents. A considerable number of American species are 
described, and among them several which are likewise described in this volume. For 
want of sufficient time, I am compelled to defer a full notice of these to the future 
portions of this work devoted to the corals. 
In the present volume I have attempted no separation of the true corals from the 
bryozoid forms, the whole being included under the denomination of Corals. The limit, 
indeed, does not yet seem to be well determined, and the characters sometimes relied 
upon fail in the examination of a large number of species. The arrangement in the plates 
of this volume, and the order of description among the species, with the exception of two 
Monographic des Polipiers Fossiles des Terrains Palseozoiques. 
