CHIM^ROIDS. 



33 l 



PARTIAL RESTORATION OF THE BERRY-BONE FISH. 



(From A. S. Woodward, Cat. Foss. Fishes, Brit. Mus.) 



The fore-limbs were either rudimental or wanting ; but a pair of pelvic fins were 

 developed. Most or all of the forms may be included in the single family 

 Coccosteidce; and 

 among these the 

 typical genus is dis- 

 tinguished by the 

 absence of any 

 pectoral fin, while in 

 the allied Br achy - 

 dims this appendage 

 is represented by a 

 hollow spine. In both these the sockets of the eyes form notches on the sides 

 of the skull ; and the same is the case with the gigantic Dinichthys of the North 

 American Devonian. In another group, however, as represented by Homosteus, the 

 eye-sockets were completely enclosed in the membrane-bones with which the head 

 is covered. 



The Chiivleroids, — Subclass Holocephali. 



Represented by three existing marine genera, of which one has three, the second 

 one, and the third two species, and a number of extinct types, the chimaeroids form 

 a second subclass, agreeing with the lung-fishes in their solid (autostylic) skulls, 

 but differing by the total absence of membrane-bones, and their superficial external 

 resemblance to sharks. The skeleton is cartilaginous, with the notochord either 

 persistent, or constricted and surrounded by cartilaginous rings, which are some- 

 times partly calcified ; and in the adult the skin is frequently quite naked, although 

 in the young it may bear on the back a series of structures similar in composition 

 to teeth, some extinct forms having plates of the same nature. In the existing 

 members of the group the optic nerves simply cross one another, and the intestine 

 has a spiral valve ; while further resemblances to the sharks are shown by the 

 presence of claspers in the males, and also by the large size and small number of 

 the single eggs. The four gill-clefts open externally by a single aperture on each 

 side, protected by a fold of skin containing a cartilaginous operculum. The mouth 

 is situated at the extremity of the muzzle, and the teeth on the palate and lower 

 jaw are molar-like, while there is also a small pair of cutting vomerine teeth in the 

 front of the upper jaw; the whole dentition thus closely corresponding to that of 

 the lung-fishes, although there are two pairs of upper palatal teeth, which present 

 certain hardened areas known as tritors. The pectoral fins are shortened, without 

 the segmented axis of the lung-fishes ; and the first dorsal fin may have a movable 

 spine articulated to the spinous processes of the vertebrae. The sides of the body 

 show a lateral line; but there is no air-bladder, and the nostrils do not open 

 behind into the cavity of the mouth. It has been suggested that the chimaeroids 

 indicate a degenerate group nearly allied to the lung-fishes, which have lost the 

 membrane-bones of the latter, and acquired a superficial resemblance to sharks. 



The ugly fish, to which the name chimaera has been applied {Chimcera 

 monstrosa), together with two other existing species, typically represents the 

 family Chimceridce, which alone has survived to the present day. The family is 



