SHARKS AND RAYS. 



colour is brown with marble-like markings of a lighter shade, often silvery-white. Behind the head 

 rises the first dorsal fin, hardly separate! from the second dorsal which extends all down the body. 

 These fins have sometimes been compared in appearance to a mane. The large pectoral fins are 

 remarkable for having their central portions fleshy, as in the Australian Ceratodus. The eggs are 

 contained in very large leathery cases, the edges of which are like velvet. The male fish is 

 distinguished by having jointed claspers, which are armed with small spines, and carries a very 

 remarkable crest on the front of the head. The teeth are altogether unlike those of other fishes, 

 since they consist of minute denticles firmly massed together into large tabular plates, which are 

 inseparably blended with the jaws. The jaw-bones are well ossified, and have no trace of the cellular 

 texture so characteristic of the bones of Plagiostomatous fishes about to be described. 



The Chimcera colliei is known from the west coast of North America, and the Chimcera affinis 

 from the coast of Portugal. 



The second Chimaeroid genus Callorhynchus is found only at the Cape of Good Hope and 

 in the Southern Pacific. The only known species is named antarcticus. It is distinguished from 

 Chimsera by having a remarkable cartilaginous prominence upon the snout, which terminates in. a 

 flap of skin. There is the same long and strong spine in front of the first dorsal fin. The extre- 

 mity of the tail, which has an upward turn, has a fin along its lower edge, while the Chimsera has 

 a low fin both above and below the tail. The anal fin. is better developed than in the Chirnaera. The 

 pectoral fins are remarkable for their large size. The young have a double sei-ies of small dermal 

 spines on the crown of the head and on the back of the body and tail ; but as the animal grows 

 older they become more or less hidden by the skin, or otherwise disappear. The upper part of the 

 body in the young is always black, with more or less of white markings and spots, but in the adult 

 there is a blackish lateral band. The claspers are almost cylindiical, and have a channel running 

 down the interior, which opens by a lateral slit. In the true Chimseras the clasper of the male is 

 usually divided into two branches, which differ in form in the different species, and the inner branch 

 io again subdivided into two, so that the clasper is tripartite. 



ORDER IV. PLAGIOSTOMATA, OR FISHES WITH OBLIQUE MOUTHS.* 



Sharks and Rays form one of the natural divisions or orders of fishes which is named the 

 Plagiostomata. The skin is rarely covered by overlapping scales ; if it is covered at all with 

 defences, they usually take the form of a rounded boss, from which a little spine, resembling a tooth, 

 rises. This covering constitutes the shagreen of Sharks, and the scales were termed by Agassiz 

 "placoid." Besides these, the body sometimes carries bony defences, which ai-e usually placed in 

 front of the fin, sometimes on the back, or occasionally on the tail. The vertebrae of Sharks 

 usually consist of two thin cones, which 

 join each other point to point, and are 

 connected together by bony plates, which 

 radiate from the centre to the circum- 

 ference of the inter -space between the 

 cones, and are at right angles to their 

 surfaces. In the Rays the vertebrae are 

 united in the fore part of the body into 

 a continuous bony mass, resembling the 

 sacrum in the hinder part of the body of 

 mammals and birds. Among some Sharks 

 the slender arches over the bodies of the 

 vertebrae are sometimes twice as many as 

 the centra. Many of these fishes have 

 the end of the tail bent upward, and the 

 fin is entirely below this bent portion. 

 These fishes are termed Heterocercal, but some Sharks have the tail more nearly symmetrical, 

 and approach the Homocercal type of bony fishes. In the Plagiostomata the brain-case is formed 



* n-Aoyto?, slanting, oro/uo, mouth. 



194 



DIAGRAM OF BRAIX OF SKATE. 

 A, Upper View ; u, Side ; c. Under ; D, Section. 



