354 SKLACKOIDEI. 



(iroup 0. Teeth small, either with a centred ruqt ""'^ **'"' o'' '"'*' 

 snuiU lutercd cvsps, or obtuse, the ciisi^s heimj otisohte. 



C. Mustelina. 



1. A jrit (it the root of the tail; a small pit hehind the aiujU of the mouth. 

 Spiracles none 8. Trianodon, p. 383. 



2. No jnt at the root of the tail ; labial folds icell developed. 



Spiracles none ; teeth with acute cusps . . 9. Leptoearcharias, p. 381. 

 Spiracles small; teeth with acute cusps. . 10. Triaeia, p. 384. 

 Spiracles small ; teeth obtuse 11. 3Iustelus, p. 385. 



Fam. 2. LAMNID.E. 



No nictitating membrane. An anal fin ; two dorsals, the first 

 opposite to the space between pectorals and ventrals. Nostrils 

 not confluent with the mouth, which is inferior. Spiracles none, 

 or minute. 



Group A. Teeth large or of moderate size. On each side of the 

 upper jcmi, at some distance from the si/mp>hysis, there is one or 

 two teeth conspictioxtsi if smcdler than the others. 



A. Lamnina. 



1. Gill-openings vo-i/ wide; side of the tail tvith a keel. 



Teeth lanceolate, not serrated 12. Lanma, p. 389. 



Teeth triangular, serrated 13. Carcharodon, p. 391. 



2. Gill-opcni/ie/s of moderate ividth ; side ef the tail without keel. 



Teeth large, awl-.shaped, with small additional basal cusps. 



14. Odontaspis, p. 392. 

 Teeth of moderate size, triangular, not serrated. 



15. Alopecias, p. 393. 



Group B. 2\'et7i very small, numerous, conical, simple. Gill-openings 



very wide B. Selachina. 



Side of the tail with a keel 16. Selaehe, p. 394. 



[Teeth very snudl, tricuspid. Gill-openings rather narrow. 

 First dorsal very low and long 17. Psetidotriacis, p. 395.] 



Fam. 3. RHINODONTID^.. 



No nictitating meratrane. An anal fin; two dorsals, the 

 first nearly opposite to the ventrals. Mouth terminal. 



Side of the tail with a keel 18. lihiiwdvn, p. 39G. 



