SQUALID^. RAFINESQUe's GENERA. 131 



9. Hexanchus. Spiracles two : branchial apertures 

 six on each side : dorsal and anal fin single : tail un- 

 equal^ oblique. — Ohs. The lesser number of the branchia^ 

 and the presence of spiracles^ distinguishes this genus 

 from that of Heptranchias, although both have a single 

 dorsal fin. This is founded on the description of the 

 Squalus griseus of Lacepede ; which^ as it is not a native 

 of Sicily^ nor appears to have been seen by our author, he 

 does not describe. 



10. Etmopterus. Spiracles twOj round : dorsal fins 

 two, laciniated — the first armed with a spine, the second 

 nearly opposite to the vent ; no anal fin : branchial aper- 

 tures three on each side : tail unequal, laciniated, ob- 

 lique : muzzle obtuse : nostrils with appendages : teeth 

 small and acute : eyes oval, and deep sunk. This genus, 

 and the Squalus squatinus Linn., have the least number 

 of branchial apertures among the whole of the Squali. 



(115.) It is much to be regretted, at the present day 

 that some of these genera have not been more fuUy de- 

 scribed : but it is also true that most of these descrip- 

 tions are sufficient to identify both the genera and the 

 species ; and that they are even more precise than those 

 which were in use twenty-five years ago. It is very 

 easy to attempt to reconcile some of these genera with 

 others of their congeners, by attributing inaccuracy to 

 the author ; and this has been done, in numerous in- 

 stances, by Cuvier — with what degree of truth will 

 hereafter appear : but even if we suppose our author 

 may have overlooked some points, and have been mistaken 

 in others, there are, nevertheless, some of these genera 

 whose structure is altogether unique, and too remarkable 

 to be either confounded or misrepresented ; among these 

 are Isurus, having an equal lunate tail ; Dalatias, 

 having spiracles, but no anal fin ; Cerictius, possessing 

 horn-like appendages ; and Etmopterus, with only three 

 branchial apertures.* Until the existence of such fish 



* Upon this alleged fact, M. Cuvier says, " Our author is most probably 

 mistaken, for he describes the Squalus squatina of Linnseus as also having 

 but three, whereas it has five." But before we can make up our minds on 

 this subject, it will be necessary to show that there is not a species, also, 



K 2 



