THE CHIM&ROIDS 



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type; the skull having numerous membrane bones. The teeth are very similar 

 to those of the Australian lungfish, but may be ornamented with small ridges and 

 pustules. 



THE BERRY-BONE FISHES Order ARTHRODIRA 



The extraordinary Palaeozoic group typically represented by the berry-bone fish 

 (Coccosteus] of the Scottish Devonian differs from the true lungfishes in that in 

 place of scales the fore part of the body is protected by large bony plates, of which 

 one pair is articulated by a hinge to the hinder part of the skull, which is likewise 

 invested with bones bearing a similar pustular or berry-like sculpture. 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 Coccosteida; and among 

 these the typical ge- 

 nus is distinguished 

 by the absence of any 

 pectoral fin, while in 

 the allied Brachydi- 

 rus this appendage is 

 represented by a hol- 

 low 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 inclosed in the mem- 

 brane bones with which the head is covered. 



PARTIAL RESTORATION OF THE BERRY-BONE FISH. 

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



THE CHIM^ROIDS 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 chimae- 

 roids form a second subclass, agreeing with the lungfishes 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 

 sometimes partly calcified; and in the adult the skin is frequently quite naked, al- 

 though in the young it may bear on the back a series of structures similar in com- 

 position 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 



