316 Prof. Hitchcock on Ichnolithology, or Fossil Footmarks. 



might possibly have been made by Crustaceans. But 1 am inform- 

 ed especially by Mr. James D. Dana, that these animals never 

 advance in such a manner as to produce impressions resembling 

 those on the rock. It would seem as if these must have been 

 made by an animal extending its didactylous feet almost at right 

 angles to its body, so as to make a row of tracks on each side. 

 For we shall find that several of the rows of tracks on fig. 9 

 correspond to each other. Thus the row A B corresponds to 

 E F ; C D to L M, and G H nearly to N O. There are indeed a 

 few tracks upon this slab which could not be brought into such 

 an arrangement, but they may belong to other rows partially ob- 

 literated. Yet I have so little confidence in any suggestions I 

 can make as to the tribe of animals by which these impressions 

 were made, that I shall describe them without a name, presuming 

 however that it must have been some animal that crawled along 

 the bottom of the ocean. 



Description. — Rows of tracks two ; parallel ; about a foot 

 apart. Feet didactylous ; toes diverging about 40° ; unequal in 

 length, blunt ; length from two to three and a half inches ; lying 

 nearly at right angles to the direction in which the animal moved. 



I ought not to omit to mention, that in many points there is 

 a striking resemblance between the impressions just described, 

 and the Ichthyopodolites described by Dr. Buckland, and noticed 

 in another part of this paper. The bluntness of the impressions 

 in New York seems, moreover, to be a strong objection to their 

 having been made by the fins of any such fish as now inhabits 

 the ocean. 



I have been struck, also, with a paper read by Mr. Pearce be- 

 fore the London Geological Society, in March, 1843, on the loco- 

 motive and non-locomotive Crinoidea. The foot in the former 

 class is sometimes bifurcated and terminated in a minute blunt 

 point. It is possible that here we may have the origin of the 

 marks under consideration.* 



CLASSIFICATION OF FOOTMARKS. 



Having now given all the facts concerning footmarks with 

 which I am acquainted, I offer the following systematic arrange- 



* Phil. Mag. for January, 1844, p. 58. 



