ANALOGIES OF THE SQUALIDiB. l6l 



only remai?kable difference between their snouts consists 

 in the one having bony or tooth-like processes, while 

 that of the other is smooth : but this difference is a very 

 important one, because no fissirostral or aquatic types, 

 whether among birds or quadrupeds, have the snout 

 horned.* The spined processes, therefore, of Pristis, 

 placed on the snout, are completely analogous to the 

 horns of ruminating quadrupeds, and to the prickles 

 on the prolonged frontal lobe of Chimcera; and both re- 

 present, however imperfectly or obscurely — for how 

 could it be otherwise ? — the rasorial birds, and the 

 ungulated quadrupeds. Between Crossorhinus, Squatina, 

 and the Sturionidce, the analogy is very slight; since 

 the only resemblance to be traced between them, at 

 present, is their mutual possession of cirri, or fleshy 

 barbs, round their mouths. We should almost have he- 

 sitated — indeed still hesitate — in definitely placing 

 Squatina among the sharks; because it seems to have, in 

 its general aspect, as already observed, a much nearer 

 affinity to the rays. Lastly, we come to the resemblance 

 between the ZyganidcB and the PolyodonidcB, which 

 agree in this one fact, — that both have the broadest heads 

 or snouts of all the groups we have been comparing. 

 The forms of the two fishes are certainly dissimilar ; 

 because the snout of Polyodon is, although very wide, 

 more remarkable for its length ; while that of the 

 hammer-headed sharks is very short and obtuse, yet 

 excessively wide. It is clear, however, that, as both are 

 fissirostral types, they represent each other; although we 

 by no means feel confident that the precise situation we 

 have assigned to the ZyganidcB is the correct one. 



(143.) The peculiar difficulties, already adverted to, 

 in our attempt to arrange the sub-families of Squalince 

 and Centrincs in their natural series, and to designate 

 their primary divisions or genera, bring with it corre- 

 sponding difficulty and uncertainty in attempting to trac- 



* The Ceratodon (Monodon monoceros), although in the aquatic order 

 of Mammalia, is but a representation of the rasorial or ruminating type 

 among the Delphinidis, or porpoises, 



VOL, I. M 



