FISHES OF THE CARBONIFEROUS SYSTEM. oN 
THE STRUCTURE AND RELATIONS OF EDESTUS. 
The first of the remarkable group of fossils now included in the genus 
Edestus was brought to the notice of scientists by Dr. Joseph Leidy, in his 
description of Hdestus vorar The type specimen was only a fragment of 
an organ that must have had a length of a foot or more by four inches in 
width and one and a half inches in thickness. The portion figured by 
Professor Leidy seems to have come from about the middle, and consists of 
a mass of bone composed of a series of segments, each of which carries at 
its upper margin an enameled, compressed, triangular, crenulated denticle 
one and a half inches in height and breadth. In general aspect these den- 
ticles considerably resemble the crenulated teeth of Carcharodon, but show 
this marked difference, that like all the cutting teeth of sharks these latter 
are flattened on one side, arched on the other, and terminate below in a 
bony base that had only a ligamentous attachment to a cartilaginous jaw ; 
hence in death and decomposition the teeth were generally separated and 
scattered. In Edestus, however, the denticles are firmly anchylosed to a 
bony support. 
At the meeting of the American Association held in Providence in 
1855 another and quite different species of Hdestus was exhibited by Prof. 
Edward Hitchcock. It was considered by him to be “the jaw of a shark, 
but of very peculiar character.” Prof. Louis Agassiz, who was present, ex- 
amined the specimen, and gave it as his opinion that it formed a part of the 
jaw of a shark allied to the sawfish. He stated that “the sword of Pristis 
is orginally composed of two bones, and if these should continue separated, 
each part, with teeth only on one side, would not be much unlike the fossil.” 
He suggested that the fish had a corresponding jaw projecting from the op- 
posite side of its head, and that both formed a powerful weapon of offense. 
He regarded it as belonging not only to an undescribed genus, but to a new 
family of fishes. 
This specimen was obtained by the Rev. John Hawks in Park County, 
Ind., “in a layer of shale overlying a coal seam.” Subsequently it was 
submitted by Dr. Hitchcock to Prof, Richard Owen, of London, who dis- 
1 Jour. Acad. Nat. Sci. Phila., 2d series, vol. 3, 1856, p. 159, pl. 15. 
