FISHES OF THE CARBONIFEROUS SYSTEM. 189 
outer margin of the jaw, and the great teeth planted in shallow sockets 
are in pairs, while in Celosteus the marginal ridge is without teeth and 
the great laniaries set along the interior shoulder are single and nearly 
equidistant. 
The difference which the jaw before us exhibits from that of Rhizodus 
is still more strongly marked, though there is a similarity of plan in their 
construction. The teeth in Rhizodus form two rows, as in Dendrodus, and 
the large ones which compose the inner row are also sometimes in pairs. 
Dr. Traquair has shown’ that the jaws of Rhizodus are segmented; a suture 
separating that part which bears the anterior laniary tooth from that which 
earries the second pair, and this from the others, ete. 
The teeth of Celosteus are strong, conical, straight, acute and smooth 
above, plicated below; they have the complicated interior structure of the 
teeth of Dendrodus, but differ from these in being plicated only at the base. 
In the latter character they agree with the teeth of Rhizodus, but are appar- 
ently less compressed and straighter. 
We have found as yet too little of the bony structure of Celosteus to 
warrant any positive statements in reference to its zoological affinities, and 
yet there are some points which have come under our observation which 
are quite remarkable, and such as suggest further examination when more 
material shall be obtained. 
The hollowness of the bones has already been noticed as a striking 
feature in their structure, and it may also be said that the bone tissue pre- 
sents a granulated appearance, which is much like that of the prismatic carti- 
lage we sometimes find representing the outlines and in part the substance 
of the skull and jaws of certain fossil Elasmobranchs; e. g., Diplodus in the 
Coal Measures, in which parts of the skeleton were partially ossified, though 
the tissue retained the granular structure of cartilage. The mode of attach- 
ment of the teeth in Celosteus is also peculiar and in some respects shark- 
like. In all the Elasmobranchs the bony and enameled teeth are attached 
to the jaws by ligaments and the jaw tissue is sometimes molded onto the 
base of the teeth, giving them greater firmness. A similar mode of attach- 
ment of the teeth obtained in Dendrodus and apparently in Rhizodus, but in 
1 Annals and Mag. Nat. Hist., April, 1877, 
