14 SELACHII : SQUALL IV. 



SUBCLASS SELACHII. (THE SELACHIANS.) 



This group, sufficiently defined above, includes two orders, the 

 Sharks and the Rays, marine fishes of large size, abundant in 

 most seas. (Gr. o-e\a\o?, shark.) 



Orders of Selachii. 



a. Gill openings lateral SQUALI, 4. 



aa. Gill openings ventral RAI.E, 5. 



ORDER IV. SQUALI. (THE SHARKS.) 



The typical sharks are elongate in form, quite unlike the skates 

 in appearance. Intermediate forms connect the two groups so 

 closely that the position of the gill openings is the only constant 

 character by which the two orders can be separated. (Lat., a 

 shark, from Gr. yaXeoy, allied to ya\fr), a weasel.) 



NOTE. The Sharks are mostly fishes of the high seas, and any of the 

 larger Atlantic species may stray to our coasts. Besides those here described, 

 the following have been at least once taken within our limits : 



Echinorhinus spinosus (Gmelin), Cape Cod; Centrocyllium fabricii (Rein- 

 hardt), off Gloucester; Centroscymnus coelolepis (Bocage & Capello), Glou- 

 cester; Pseudotriacis microdon (Capello), Long Island; Aprionodon isodon 

 (Muller & Henle); Isogomphodon limbatus (Muller & Henle), Wood's Holl. 



Omitting extralimital families, we have the following analysis of 



Families of Squall. 



c. Pectoral fins moderate, without deep notch at base in front; gill openings 5. 

 b. Anal fin wanting. 



c. Dorsal fins each with a stout spine SQUALTD.F,, 4. 



cc. Dorsal fins without spine. . . , SOMNIOSID.E, 5. 



bb. Anal fin present ; both dorsals without spine, the first inserted before 

 -" the ventrals. 



d. Caudal fin not lunate, the upper lobe very much longer than the lower, 



with a notch below, towards its tip; side of tail without keel. 

 e. Last gill opening above base of pectoral. 

 /. Tail moderately developed, not half length of rest of body ; eyes 



with nictitating membrane. 



g. Head kidney-shaped or hammer-shaped, much wider than long. 



SPHYRNID^E, 6. 



gg. Head normally formed GALEORHINID^:, 7. 



ff. Tail very long, as long as rest of body; no nictitating mem- 

 brane. ALOPIID^E, 8. 



