124 



PALEONTOLOGY. 



size of the marginal teeth, and their close resemblance to the 

 jaw-teeth of Carcharias, their enamelled border being finely 

 denticulate. I am indebted to Professor Hitchcock, of Am- 

 herst College, U.S., for the oppor- 

 tunity of examining this most 

 rare aud singular fossil, first made 

 known by Leidy, as being pro- 

 bably part of the jaw of a shark, 

 for which, therefore, he proposed 

 the name Edestes, signifying de- 

 voured If my determination of 

 its nature be correct, it has formed 

 part of a fish more liable to be 

 devoured, and needing unusual 

 defence against some larger con- 

 temporary shark.- The true jaws 

 and teeth of Edestes may one day 

 be discovered, and throw light 

 upon its habits and affinities. 

 The other plagiostomous genera based upon fossil spines from 

 the coal formations are — Oracanthus, Gyracanthus, Nemacan- 

 thus, Cosmacanthus, Leptacanthus, Homacanthus, Trystichius, 

 Asteropterycliius, Physonemus, Sjrfien acanthus, Platy acanthus, 

 Dipriacantlvus, Erismacanthus, Orthacanthus, Cladacanthus, 

 Lepracanthus. 



Immediately above the coal measures lie a variable series 

 of sands and clays of different colours, including the coal 

 plants ; above this, a marl slate in thin layers, containing 

 scanty evidences of fishes ; but these are more abundant and 

 instructive in the superincumbent magnesian limestone, in 

 which formation, near Belfast, ichthyodorulites of the genus 

 Gyropristis (Ag.) have been found. Above this are the penean 

 red sandstones, in which, at Westow, have been found fossil 

 spines closely allied to, if not identical with, the Gyracanthvs 



Portion of Spine, 

 Edestes. 



(Coal, Indiana.) 



