HOLOCEPHALA. 349 



small " placoid " spines, which occupy the median line of the 

 back, and remind us of similar dermal productions in the 

 Eays. The males, besides, are provided with a singular erectile 

 appendage, spiny at its extremity, and received in a groove 

 on the top of the head. On the other hand, the relations of 

 the Chimaeras to the Ganoid, and, more especially, Dipnoous 

 type become manifest in their notochordal skeleton and con- 

 tinuity of cranial cartilage. The spine in front of the first 

 dorsal fin is articulated to the neural apophysis, and not merely 

 implanted in the soft parts, and immovable as in Sharks. A 

 cartilaginous operculum makes its appearance, and the 

 external gill-opening is single. The dentition is that of a 

 Dipnoid, each "jaw" being armed with a pair of broad dental 

 plates, with the addition of a pair of smaller cutting teeth in 

 the upper "jaw." Fossils of similar dental combination are not 

 rare in strata, commencing from the Lias and the bottom of 

 the Oolitic series ," but it is impossible to decide in every case 

 whether the fossil should be referred to the Holocephalous or 

 Dipnoous type. According to Newberry, Chimairoid fishes 

 commence in the Devonian with Bhynchodits, the remains 

 of which were discovered by him in Devonian rocks of Ohio. 

 Undoubted Chimseroids are Elasrnodus, Psaliodus, Ganodus, 

 Ischyodus, Edaplwdon, and Elasmognathus, principally from 

 mesozoic and tertiary formations. Very similar fossils occur 

 in the corresponding strata of North America. A single 

 species of Callorhynclius has been discovered by H. Hector 

 in the Lower Greensand of New Zealand. 



The living Chimseras are few in number, and remain 

 within very moderate dimensions, probably not exceeding a 

 length of five feet, inclusive of their long filamentous, diphy- 

 cercal tail. They are referred to two genera. 



ClIiMiERA. — Snout soft, prominent, without appendage. The 

 dorsal fins occupying the greater jiart of the back, anterior with 

 a very strong and long spine. Longitudinal axis of the tail nearly 



