142 CLASSIFICATION OP FISHES. 



which blends into the next sub-family of Centrince, and 

 we are consequently prepared to expect that the chief 

 characters of the two groups also blend into each other : 

 in this expectation we are not disappointed, for we find 

 that the presence or absence of spiracles now becomes 

 quite a secondary character. In the true type, which 

 is probably Isurus, there are no spiracles; but in Lamna 

 they first appear (perhaps not in all the species*) to be 

 minute ; and in Selachus we still find them very small. 

 In all these, however, we see the three primary charac- 

 ters already noticed. Isurus, however, stands promi- 

 nently forward as a most remarkable type, having the 

 snout so lengthened and pointed as to be a representative 

 of Pristis: in Lamna, the snout, although not lengthened, 

 is still pointed and conic ; and even in Selachus, the muz- 

 zle, according to Cuvier, projects far beyond the mouth. 

 What other sub-genera enter into this group, we know 

 not ; but it is quite clear that we have now a passage 

 opened to the spiracled sharks. Before, however, we 

 quit this division, we may advert to another form, 

 which seems entitled to be viewed in the light of a 

 generic type ; for, although only one species is yet 

 known, its form is so remarkable, and so different from 

 all others, that it must either be placed with the Squatince, 

 or stand as the most aberrant genus in the present as- 

 semblage. We allude to Rineodon of Dr. Smith, having 

 all the characters, as it would appear f, of Selachus, but 

 with the mouth on the top of the snout. As this struc- 

 ture is totally at variance with that of the ordinary 

 sharks, excepting Crossorhinus and Cestracion, we may 

 fairly conclude, from the location that has been assigned 

 to it, that it has a relation both to those and to Squatina. 

 In the Crossorhinus lobatus M. andH.(^r. 15.)orWatts's 

 shark, the mouth is also terminal, but the sides are fur- 

 nished with broad cirri, or lobes. This singular fish 



* This supposition is highly probable, and will at once reconcile the oppo- 

 site statements of Cuvier and Dr. Smith, 

 t Mag. of Nat. Hist. No. xiii. p. 37. second series. 



