On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 419 
being punctate, with minute tabular structure. The surface of the Cochliodonts is 
similarly punctate and tabular in structure, and with modification it rises into 
external folds and ridges.. So far as known, the entire skeleton of Cochliodus was 
more or less cartilaginous, and except in rare instances, where a portion of the 
mandible has been preserved, the skeleton of this group remains unknown and 
unpreserved. 
Professor Miall (op. cit., p. 26,) discusses the probable mode of growth of the 
teeth of Ceratodus, and concludes that “it is probable that the tooth was at first 
comparatively soft and vascular, that it grew, replaced the loss from wear, and 
changed its figure as requisite, becoming fully calcified and rigid only in the adult.” 
After careful comparison of the teeth of Ceratodus with those of the Cochliodonts, it 
will be found that the teeth of the former resemble the latter to this extent, that 
the several ridges or denticulations radiate more or less froma central point on 
the smooth hinder surface of the tooth to its anterior or outside margin. It has 
already been shown that the teeth of Cochliodus increase in size by the growth 
or addition of new dental substance to the constantly expanding inner surface of 
the tooth, giving it a convoluted form. In some other members of the group, 
as in Psephodus, &c., a similar plan of growth results in a radial expansion of the 
surface, wh'lst, at the same time, it maintains a depressed and flattened surface. 
It is possible that the outer denticulated margin of Ceratodus increased in the same 
way, the teeth increasing in size with the growth of the jaws to which they were 
attached. The method of growth here indicated, though matter of speculation, is 
perhaps more in consonance with observed facts, than the idea suggested that the 
teeth remained in a soft state until mature. The observation made by Professor 
Miall, that the posterior portion of the teeth would be much worn, and that lines 
showing the repeated additions to the surface should be apparent, is not of great 
value. It may be seen in a number of any of the genera of the Cochliodonts, that 
in most specimens the lines indicating growth are worn off, whilst in other 
specimens they are distinctly visible, parallel with the margin of the newer portion 
of the tooth. In the case of Ceratodus, the tooth being more than usually flat, 
and the new surface immediately exposed to the triturating action of the opposing 
tooth, it will easily be conceived that the lines, if any, might be removed. With 
regard to the first portion of the objection, the posterior or angular portion of the 
teeth of Ceratodus are usually smooth, without ridges, and apparently considerably 
worn. 
The Cochliodonts, usually regarded and described as closely related to the 
Cestracionts, with very great modifications of the dentary arrangement, have been 
found to differ from that group in the following particulars. The jaws are joined 
in front with a wide symphysial space, probably edentate. In Cestracion the anterior 
portion of the jaws is greatly produced, and is armed with a median row of sharp 
cutting teeth, with several others ranged on each side; the difference in the 
