J 00 PROF. D. M. S. WATSON AND MR. E. L. GILL ON THE 
Plate 76, figs. 1-11, marginal ossicles, but including some ordinary roof-bones of small 
fisbes, e.g. fig. 5, squamosal; 3, intertemporal: fig. 14, left intertemporal; 12, 19, 
circumorbitals ; 20; 1. " tabular " ; 22, r. intertemporal ; 24, 1. squamosal ; 25, 1. 
frontal; 27, r. " tabular " : 28, r. squamosal, underside ; 29, 1. frontal, underside ; 
32, 1. " tabular," underside, with one of its lateral bones ; 33, nasal, underside ; 
34, fragment of squamosal ; 37, marginal ossicles; 89, r. nasal. 
Plate 77, fig. 17, " tabular." 
Plate 78, fig. 6, post-temporal. 
Ctenodus, Agassiz. 
The genera Ctenodus and Sagenodus were separated primarily on the 
characters of the tooth-plates, though when Owen first pubUshed the name 
Sagenodus he was under a misapprehension as to the nature of the tooth- 
section on which he founded it. Since the publication of Dr. Smith 
Woodward's "Catalogue of Fossil Fishes " (vol. ii., 1891), the name Ctenodus 
has been generally applied to tooth-plates uith about 12 or more ridges, 
roughly parallel, as contrasted with the others ( Sagenodus) having fewer, 
usuall)^ 6 or 7, ridges, with a strongly-marked radial arrangement. If this 
were the only distinction between the two genera it would be difficult to 
maintain, since tooth-plates of intermediate character occur in the Lower 
Carboniferous of Edinburgh. There are, however, many other distinctive 
characters independent of the difference in the teeth ; and in spite of a 
general resemblance which shows the two genera to be nearly related, the 
additions which we are able to make to what was known of each of them 
tend still further to justify their separation. 
Sagenodus having been dealt with already, Ctenodus can be sufficiently 
described, with the aid of figures, on brief and comparative lines. 
In most or all of the beds and horizons from which we have had material 
for examination, remains of Ctenodus are much less abundant than those of 
Sagenodus, and there is consequently more difficulty in ascertaining its 
skeletal structure with completeness. In particular there is in the collections, 
up to the present, an almost entire absence of specimens such as were of the 
greatest help in the case of Sagenodus, namely slabs bearing the scattered 
remains of some considerable part of an individual fish. We have never yet, 
for example, seen any considerable part of the shoulder-girdle of Ctenodus 
in "association with other portions of its skeleton, and the bones which we 
take to be those of its shoulder-girdle are assigned to it without absolute 
proof, tiiough on strong grounds of probability. 
The fishes of the genus Ctenodus were of decidedly larger average size 
than those comprised in Sagenodus. Nine or ten inches is a usual length for 
skulls of Ctenodus, as compared with five or six inches for skulls of 
Sagenodus. 
