354 PALEONTOLOGY OF NEW-YORK. 



taceans. The other consists of a median groove or dej>ression 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 uf 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 Oiliers 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 auy vertebrate animal. It is impossible, however, to know, 

 at the present time, their true origin, and any speculative opinions regarding thein must 

 be received with caution. 



NOTE B. 



CORALS OF THE CLrSTON AND NIAGARA GROITPS. 



Since this volume has been printed, I have seen the work of Milne-Edwards and 

 Jules Haime upon the fossil corals of the palfeozoic 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 de3 Polipiers Fossilcs dea Terrains PalaDOZoiiiucs. 



