2 



BRITISH FOSSILS. 



and a conically tapering caudal extremity. The orbits are situated 

 forwards, while the gape extends far back. The frontal bones (fig. 2) 

 are distinct from one another and from the parietals, which last are 

 not shorter than the frontals, and, though in contact throughout 

 the whole length of their inner margins, are perfectly distinct from 

 one another. Three bones, or scales (for they seem to partake as 

 much of the nature of the latter as of the former), a median and 

 two lateral, roof in the occipital region. The middle of the jugular 

 region, or that comprised between the two rami of the mandible 

 upon the under surface of the cranium, is occupied by two large, 

 triangular, squamiform, bones — the 'princiioal jugular plates (j ^) ; 

 while the interval left between them and the mandibular rami, on 

 each side, is taken up by a series of smaller, quadrate plates, which 

 increase in size from before backwards — the lateral iugular plates (y). 

 There is no rhomboidal oneclicm jugular plate interposed between the 

 anterior part of the inner edges of the principal jugular plates. The 

 teeth are of two kinds ; smaller, set in a close series along the edges 

 of the jaws ; and larger, placed at intervals along the palate, and 

 perhaps along the inner side of the mandible. The larger teeth, 

 have grooved bases, and appear to be composed of dendrodentine.* 



Diagram of the Head of Glyptolccmus. — For an explanation of the letters, seep. 40. 



* Prof. Pander applies the tenn " Dendrodonts " to those fishes the pulp cavities of 

 whose teeth appear branched, in consequence of the folding of their walls; and such 

 folded dentine may be conveniently termed " dendrodentine." 



