from the Shales of the Northumberland Coal-field. 85 
- ner margin regularly and much arched, the outer only i 
curved ; the surface with six or seven strong, compressed, 
sharp-edged ridges, placed transversely in a somewhat radia- 
ting manner towards the outer margin, where, being enlarged, 
they are curved downwards and denticulated ; the anterior 
ridges are very oblique, being much inclined forwards ; the 
denticles or tubercles are much compressed in the direction 
_ of the ridges, and are lancet-formed, with sharp points ; 
they are coated with brilliant enamel in finely preserved 
specimens. ‘T'he above is the description of the palatal 
tooth ; the mandibular is narrower than the former, and is 
broadest in front, tapering pretty regularly to the posterior 
extremity ; the anterior ridge is very wide, and much pro- 
duced beyond the outer extremities of the others, and they 
are all more curved downwards than those of the palatal 
tooth. 
‘This is a very distinct form, and cannot be confounded with 
any of the other species. I have collected between forty and 
fifty specimens of it, most of which were procured from the 
Low-main shale at Newsham; the rest are from Cramlington : 
many of them have the jawbone attached in a very perfect 
condition. The palatal tooth is a little more than half the 
length of the bone, the posterior extremity of which is much 
expanded and truncated. The mandibular bone is not much 
widened posteriorly, and is about half as long again as the 
tooth. 
The specimens vary much in size, the largest being a little 
over an inch and a half long, while the length of the smallest 
is not more than three-eighths of an inch. The former has 
seven ridges, the latter six; so that it is evident that age does 
not make any material change in this respect. This is highly 
satisfactory, as we can with greater assurance assume that the 
number of ridges is a good specific character. 
The anterior portion of a fish of this species has occurred at 
Newsham, exhibiting one of the gill-opercles and two of the 
dental plates with the denticles interlocked ; numerous scales 
are also displayed, but they are in such a mashed-up state 
that the characters cannot be determined with precision. 
Enough, however, is seen to show that they agree with those 
of C. elegans, though the ridges or plaits ornamenting the 
surface are not so numerous and are considerably coarser; the 
rosette, too, in the centre of the exposed portion is not so con- 
spicuous, and seems to be smaller. The opercular plate, which 
is upwards of an inch across its longer Biccter: and a little 
more than three-quarters of an inch in the other direction, is 
thick and irregularly ovate, with the margin sinuous; the 
