242 ZOOLOGY. 



Fam. 7. Lamnini. Branchial apertures large, and anterior to the 

 pectorals. Caudal furrows evident. Caudal fin semilunate. A ridge on 

 each side of the tail. Spiracles very small. Intestinal valve helicoid. 

 vSecond dorsal, and the anal small, and opposite to each other. Ex. : Lamna, 

 Oxyrhina, Selache. S. maxima is the gigantic basking shark of the coast 

 of the united States. 



Fam. 8. Odontaspidini. Branchial apertures large, all anterior to the 

 pectorals. Anal and second dorsal large. Upper lobe of the caudal fin 

 elongated, as in Carcharias. The lateral ridge of Lamnini is wanting. 

 Ex. : Odontaspis. 



Fam. 9. Alopiadini. Snout short and conical. Spiracles very small. 

 Nostrils small, with a small valve at the upper border. No labial cartilage. 

 Branchial apertures small, the last standing over the pectorals. Teeth 

 triangular, flat, with cutting undenticulated margins, the same in both jaws. 

 Anal and second dorsal opposite, very small. Upper lobe of caudal fin 

 very long ; a furrow at its base. Intestinal canal helicoid. Ex. : Alopias. 



Fam. 10. Cestracionini. Mouth at the anterior border of the snout. 

 Nostrils extending to the mouth. Distinct spiracles. A spine before each 

 dorsal. Ex. : Cestracion. The single living species, C. philHpsii, or Port- 

 Jackson shark, is of great interest on account of the peculiarities of its 

 anatomical structure, which exhibit a close relation to many extinct forms. 



Fam. 11. Rhinodontini. Mouth and nostrils at the anterior extremity of 

 the flat head. Teeth exceedingly small, conical, very numerous. Spiracles 

 'very small. Ex. : Rhinodon. 



c. An anal, and but one dorsal. 



Fam. 12. Notidani. A median tooth in the lower jaw. Ex. : Hep- 

 tanchus, Hexanchus. 



d. Anal fin absent. 



Fam. 13. Spinicini. A spine before each dorsal. Ex. : Acanthias, 

 Spinax. PI. 81, fig. 27, represents Spinax acanthias. 



Fam. 14. ScYMNiNi. Dorsal fins without spines. Ex. : Scymnus. 



Fam. 15. SauATiNiNi. Pectoral fins very broad, the base extending to 

 the head, but separated by a fissure. At the bottom of this fissure are 

 situated the branchial apertures, which follow in close succession, and are 

 only separated by membranous laminae. Ex. : Squatina. 



Sub-order 2. Raiadcs. 



Fam. 16. Pristidini. Body elongated; snout prolonged into a long 

 saw, with teeth implanted in the two edges. Ex. : Fristis. Pristis anti- 

 quorum is the saw-fish found in various parts of the globe {pi 82, fig. 2). 



Fam. 17. Rhinobatini. Body rhomboidal, elongated ; tail thick, fleshy ; 

 dorsal fins two, remote ; caudal fin terminal ; teeth minute, paved, arranged 

 in quincunx. Ex. : Rhinohatus. 



Fam. 18. Torpedinini. Body orbicular ; head margined by the extended 

 pectorals ; tail thick, depressed at the base, moderately long, the fin termi- 

 nal, large, triangular ; teeth small, acute ; a peculiar electrical apparatus in 

 446 



