ANGEL- AND SAW-FISHES. 535 



becomes so intent on its occupation as to allow itself to be harpooned without 

 attempting to escape. Four living young are stated to be produced at a birth. 

 Finally, we have the spiny shark (Echinorhinus spinosus) of the Mediterranean 

 and Atlantic, which while agreeing with the last in the small size of the fins and 

 the absence of spines to the dorsals, differs by the teeth being alike in both jaws, 

 and by the presence of large rounded tubercles scattered over the skin ; the body 

 being very bulky, and the tail short. This shark lives at considerable depths, and 

 but rarely comes to the surface. 



THE EXTINCT PETALODONTS, Family PETALODONTID^. 



The extinct genera Petalodus and Janassa, together with several other allied 

 types from the Carboniferous rocks, represent a family apparently connecting the 

 last with the more typical rays. In these fishes the body is moderately depressed, 

 and the pectoral fins are large and continued anteriorly towards the head. The 

 teeth, which generally have large roots, are compressed from front to back, with the 

 crown more or less bent backwards, and either with a sharp cutting-edge, or very 

 blunt. In the mouth they were arranged in straight rows to form a pavement. 



THE ANGEL-FISH, Family SQUATINID^E. 



The sole existing representative of its family, the angel-fish, or monk-fish 

 (Squatina vulgaris), constitutes, so far as external form is concerned, a kind of 

 connecting link between the sharks and the rays. Having the body as much 

 depressed as in some of the latter, the angel-fish differs in the nearly terminal 

 position of the mouth, and also in the circumstance that while the basal portion of 

 the pectoral fins is much produced forwards, it does not extend so far as to join 

 the head. The wide gill-clefts are lateral in position, and partly covered by the 

 base of the pectoral fins ; the spiracles are wide and placed behind the eyes ; and 

 the teeth are conical arid pointed. Spines are wanting to the dorsal fins, which are 

 situated on the tail ; and the skin is studded with tubercles. Not unfrequently 

 growing to a length of at least 5 feet, the angel-fish has an almost cosmopolitan 

 distribution, and is by no means uncommon on the British coasts, more especially 

 in Scotland. In colour it is mottled chocolate-brown above, and whitish beneath, 

 and except that it produces living young, which may number as many as 

 twenty at a birth, its general habits are similar to those of the rays. Fossil 

 species of angel-fish range through the Tertiary and Cretaceous strata to the 

 upper Jurassic. 



THE SAW-FISHES, Families PRISTIOPHORID^E and PRISTID^:. 



Unique among the whole class on account of the production of the upper jaw 

 into a long flattened beak, furnished on either edge with a series of large, sharp, 

 and pointed teeth, set in distinct sockets at a considerable distance from one 

 another, the saw-fishes form two well-defined families, the first of which approxi- 

 mates to the sharks in the position of the gill-clefts, while the second agrees with 



