from the Shales of the Narthumherland Coal-field. 349 



Low-Main Seam and Shales of Coal, Northumberland "*. 

 It has become necessary to do this, as the anticipated bene- 

 ficial results from the former " Criticism" of the " Abstract " 

 of the paper as read have not been realized f, though the in- 

 fluence of this criticism is distinctly traceable in the text of the 

 published paper, as well as in the appended footnotes. 



The first genus we have to refer to is that named Miogano- 

 dus (pi. 8), which is founded on the section of a tooth that in 

 no respect differs from that of the so-called Bhizodus lancei- 

 formis, Newberry. We have shown in the former part of this 

 communication that this reputed fish is most probably a Laby- 

 rinthodont amphibian ; but be this as it may, we have teeth 

 of this species attached to the dentary bone exactly similar in 

 contour to, and not larger than, the figure of the tooth of this 

 so-called new genvis : and when a longitudinal section of 

 these teeth is examined under the microscope, there is no per- 

 ceptible difterence in the minute structure from that of the 

 tooth of Mioganodus ; even the concentric layers of dentine, 

 which are considered characteristic, are equally well marked. 

 Certaiidy, when the tooth of B. lanceiformis is perfect, the base 

 exhibits the Labyrinthodont infolding of the peripheral wall 

 of dentine ; but wlien the tooth is found detached (and that 

 figured by Prof. Owen was so found), the basal portion is 

 rarely if ever present ; and then the dentinal walls are observed 

 to thin out from the interior and to terminate below, when 

 seen in section, in sharp wedge-shaped points, just as they are 

 represented in the figure oi Mioganodus laniarius. The tooth, 

 then, on which this genus is founded is merely the upper por- 

 tion or crown of a tooth of the so-called Bhizodus lanceiformis. 



Pihizodopsis sauroides^ sp., Williamson. 

 Several specimens of the elegant fish upon which Professor 

 Huxley founds the genus Bhizodopsis\ have occurred at 

 Newsham. They are all in a very incomplete state, though, 

 with the aid of the whole series, many of the characters can 

 be determined. The most perfect specimens are betAveen five 

 and six inches in length ; the largest is eight inches long, exclu- 

 sive of the tail, which is wanting ; and the smallest is not 

 more than two or three inches in extent. There is proof, 

 however, that this species sometimes attains a considerable 

 size: a crushed head has been found that measures nearly 

 three and a half inches in length ; and ossified vertebral rings 

 have occurred that are nine-tenths of an inch in diameter. 



* Trans. Odontological Society, 1867. 



t Geological Magazine, vol. iv. pp. 323 & 378. 



X Quart. Joiirn. Geol. Soc. vol, xxii. p. 590 (1866). 



