58 



PISCES. 



quadrate in form, the outer margin being nearly straight, sharply 

 deflected and thickened, the inner and posterior margins tapering gra- 

 dually to a thin edge; the punctate tritoral area is continuous on its 

 oral surface. The vomerine dental plate is smaller than the palatine, 

 of triangular form, broad posteriorly, and provided either with a long 

 anteriorly-directed process or with a distinct small tooth in front ; its 

 punctate tritoral area is subdivided into rounded patches. There is a 

 large spine in front of the dorsal fin, this being long and slender, 



FIG. 45. 



Hyriacanthm granulatus ; outline of fossilized imperfect head, lateral aspect, 

 showing rostral prominence, about one-third nat. size. L. Jurassic (L. 

 Lias) ; Dorsetshire, d, left mandibular dental plate, oral aspect ; md., 

 mandibular cartilage; orb., orbit; pi. , so-called palatine dental plate; r, 

 production of rostral region ; r.s, rostral spine of male. (British Museum, 

 no. 43050.) 



somewhat laterally compressed, and with a large internal cavity; its 

 sides are more or less ornamented with small tubercles, while a series 

 of large, thorn -shaped, spinous tubercles is arranged along each edge of 

 its posterior face, passing into a single median row distally, and there 

 is also a single series of similar denticles on at least part of the anterior 

 border. Nothing is known of the trunk. Myriacanthus is represented 

 only by two species, M. paradoxus and M. granulatus, in the Lower 

 lias of Lyme Regis, Dorsetshire; but several names have been given 

 to detached fragments of the fish. 



The family of Chimaeridae, which still survives, appears first 

 in the Lower Oolites, but attained its maximum development 

 in the Cretaceous arid Eocene periods. In regard to the denti- 

 tion it exhibits an advance upon the preceding families, as 



