FISHES OF THE CARBONIFEROUS SYSTEM. 219 
dreds of the segments which once composed the spines of H. Heinrichsi. 
This shale is apparently a fresh-water sediment, carbonaceous mud which 
accumulated in the lagoons of water that occupied portions of the coal 
marshes; either following a subsidence and then covering the coal, or syn- 
chronous with the peat from which the cubical coal is derived. In the latter 
case the amount of earthy matter associated with the carbon is less, and we 
then have cannel coal. Some of these lagoons must have been very large, 
and may perhaps have communicated with the ocean; for the fishes which 
bore these defensive and offensive weapons were of enormous size, and could 
not have been restricted to very narrow quarters, since they required a vast 
amount of food for their subsistence. The associated fossils include a large 
number of fish teeth, some of which beiong to carnivorous sharks, as Clado- 
dus and Petalodus, and others with crushing teeth, as Oredus, Orthopleurodus, 
ete. The habitat of Edestus would therefore seem to have been somewhat 
similar to that of Rhizodus and Megalichthys, of which the teeth, scales, ete., 
are so common in the coal shales and cannels of England and Scotland. 
Prof. Henry Woodward describes’ and figures a fossil from the Car- 
boniferous rocks of Australia, to which he gives the name of Hdestus 
Davisi. It is the impression of a bony arch about four inches long, on the 
convex border of which are set fourteen acute, compressed, lancet-shaped, 
crenulated denticles. It is more curved than the other described species of 
Edestus, but is so like them that Dr. Woodward seems to have been fully 
justified in placing it in that genus. In his discussion of the structure and 
relations of this fossil Dr. Woodward compares it with the segmented spines 
of Pelecopterus, Cope, from the Cretaceous rocks of Kansas, and is thereby 
led to consider it a pectoral defensive spine. There are, however, some 
points in the structure of this and other spines of Hdestus which will be 
alluded to farther on, that make it difficult for us to accept this conclusion. 
In August, 1887, Miss Fanny R. M. Hitchcock, an earnest and accom- 
plished student of comparative anatomy, read a paper before the Biological 
Section of the American Association “On the Homologies of the so-called 
Spines of Edestus,” in which she suggested that Hdestus was an intermandib- 
ular arch of bone carrying teeth, and most like the dentigerous arch which 
1Geol. Magazine, London, vol. 22 (1886), p. 2. 
