REMAINS OF EEPTILES AND FISHES. 81 



only specifically but likewise generically distinct from Pteroplax 

 cornuta. 



Two or three other different kinds of small sternal plates have 

 likewise been found ; but particular allusion will be made only 

 to one species, which appears to be the best characterized. The 

 others must be left for further elucidation. 



Of this species there is a set of three plates lying in juxtapo- 

 sition, apparently not very much disturbed ; two are very nearly 

 perfect, the third is partially destroyed. They are rounded and 

 somewhat elongated, particularly one, which is probably a lateral 

 plate ; it is upwards of half-an-inch long. 



In form and size these plates resemble those of Kerater2')eton, 

 and in structure they are almost identical. These specimens, as 

 well as those figured of that genus by Professor Huxley in the 

 memoir before quoted, appear to have lost the external surface, 

 and the bone fibres beneath are exposed to view, radiating and 

 anastomosing in a very regular manner from the centre of os- 

 sification, which is a little elevated. The appearance is very 

 peculiar, and not a little resembles that of some specimens of 

 Synocladia from the Magnesian Limestone. In the species be- 

 fore us the bony reticulation is not quite so fine as it is in K. 

 Ocdvani. 



Rhizodus Hibberti, sp., Arjassiz. 



The teeth of this species have not yet been found in the shales 

 of our neighbourhood ; but large scales which appear to belong 

 to it are not by any means uncommon at Newsham and Cram- 

 lington. They are rarely found perfect ; sufficient examples 

 have, however, been obtained to enable us to identify them with 

 the scales of Rhizodus Hibberti described by Dr. Young in vol. 

 xxii., p. 599, of the "Journal of the Geological Society." The 

 largest we have seen measures three inches in diameter. They 

 usually appear quite thin, and are of an ii-regularly rounded 

 form, with the front mai-gin a little flattened, the posterior a 

 little produced, and the sides only shghtly arched. The surface 

 is marked with numerous sharp concentric lines of growth, and 



F 



