ANALOGIES OF THE TWO TYPICAL GROUPS. l6'7 



(14~.) The result of this disposition of the groups is 

 seen in the preceding table, which shows the analogies 

 existing between their component parts. From these it 

 would appear that each has a division (Dalatias in one, 

 and Galeus in the other), where the ventral fin is want- 

 ing, and the dorsal fins are spined. Again, Isurus and 

 Pristiurus (which latter we have arranged with Scyl- 

 lium} are the longest-snouted sharks yet discovered : 

 while Rineodon and Cestracion represent each other by 

 the very reverse of this latter character ; for the mouth 

 of both is described as being at the extremity of the 

 muzzle ; and thus they also represent Squatina and 

 Crossorhinus. With these striking coincidences before 

 us, we need feel less regret at not being better informed 

 on the new genus Scoliodon of MM. Muller and Henle; 

 but the short characters they have assigned to it sin- 

 gularly coincide, in all but the teeth, with those of 

 Mustelus : and as this latter genus opens a passage to 

 Pristis, so we may expect that it would possess some 

 one of its characters; and this expectation is realised by 

 the structure of the teeth, which are precisely alike ; 

 Mustelus including the only sharks where these organs 

 are blunt and tesselated, as in the rays and saw-fish. 



(148.) That errors may eventually be discovered in 

 this imperfect sketch of the natural arrangement of the 

 sharks, is only what we fully expect ; and this, for the 

 reasons already stated, we should say would be inevi- 

 table. But whether these errors are few or many, 

 the main facts which we have sought to establish, of 

 there being certain types, representing each other, but 

 without mutual affinity, will remain unshaken ; and 

 further, that those types correspond to others pervading 

 every group in ichthyology. We contend not, in this 

 case, for details, or for the accuracy of minor com- 

 binations : all we seek to establish at present, is the 

 theory of representation ; and for this there seems to be 

 conclusive evidence. The two typical groups may pos- 

 sibly possess other characters than the mere absence or 



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