from the Shales of the Northumberland Coal-field. 85 



ner margin regularly and much arched, the outer only slightly 

 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. The 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 tlie 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 chai-actcr. 



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 diameter, and a little 

 more than three-quarters of an inch in the other direction, is 

 thick and irregularly ovate, with the margin sinuous ; the 



