362 TROPICAL AND SOUTHERN FISHES 



-organisms. T3oth are harmless, and the second, often called the whale-shark, 

 is the largest of the whole group, sometimes measuring as much as fifty or even 

 sixty feet in length, while the first-named, or true basking-shark, falls short of this 

 by some ten or twenty feet. The whale-shark is blackish brown in colour, spotted 

 and striped with buff. Both species are armed with quite minute teeth, and 

 have the mouth terminal instead of being situated beneath the head, as in the 

 more typical sharks. In the basking-shark the aperture of the mouth is com- 

 paratively narrow, but in the whale-shark it is so wide as to suggest the mouth of 

 a travelling-bag. 



To yet another family belongs the comparatively small shark known as the 

 spiny dog-fish (Acanthias vulgaris), which is common to the temperate seas of 

 both the Northern and the Southern Hemisphere, although unknown in the 

 tropics. This, the most common of the European dog-fishes, takes its name from 

 the presence of a bony spine in front of each dorsal fin, and is about four feet 

 in length. 



The last sharks which can be mentioned here are the comb-toothed species of 

 the genus Notidanus, and the curious Japanese frill-gilled shark, Chlamydoselache 

 anguineus, each of which represents a separate family. The comb-toothed sharks 

 take their name from the peculiar character of their teeth, each of which consists 

 •of a number of small cusps arranged in a longitudinal line, and gradually 

 decreasing in size from the first to the last. The fringe-gilled shark, on the other 

 hand, is characterised by its elongated, almost eel-like form, and the presence of 

 frill-like expansions on the five gill-arches. The comb-toothed group is widely 

 ■distributed in the warmer seas. 



The curious monk-fish, or angel-fish (Squatina vulgaris or 

 Rhina squatina), is of interest as forming a connecting link between 

 the sharks and the rays. It may, in fact, be described as a ray-like shark, that is 

 to say, a shark with a depressed body and much expanded pectoral and pelvic fins. 

 These singular fishes, for there are several species, are widely distributed in both 

 the Atlantic and the Pacific Oceans, and are believed to subsist largely on flat- 

 fishes of various kinds. 



The well-known and formidable saw-fishes of the genus Pristis 

 Saw-Fishes. ... ... 



and the family Pristidce, are really aberrant rays distinguished by 



the prolongation of the upper jaw into the ' saw,' which consists of a long, flat 



plate of bone armed on each edge with a series of long, flattened teeth set in distinct 



sockets. In addition to the typical saw-fishes, there is an allied group, the 



Pristiophwidai, which are more shark-like in character, having the gills laterally 



placed, as in sharks, instead of being situated on the under surface, as in the true 



^saw-fishes and the rays. The most common representatives of the second of these 



families are the Japanese and Australian Pristio-phorus japonicus and the 



Australian P. cirrliatus. Both are characterised by the presence of long tentacles 



beneath the saw, which are wanting in the more ray-like typical saw-fishes. All 



the latter attain large dimensions, the biggest being the giant saw-fish (Pristis 



pectinatus) of most tropical seas, which grows to twenty feet or so in length, and 



is distinguished by bearing a protuberance on the muzzle. Saw-fishes obtain their 



food by attacking whales and large fishes with sideways strokes of their 



