SQUALID^. — IV. 15 



ee. Last gill opening before base of pectoral ; dorsal fins subequal. 



Cakchaeud^, 9. 

 dd. Caudal fin lunate, the lower lobe not much shorter than the upper ; 

 tail with a keel on each side, last gill opening before pectorals. 



h. Gill openings rather large ; teeth large Lamkid^, 10. 



hh. Gill openings very large, nearly meeting both above and below; 



teeth small (largest of all fishes) Cetokhlsid^, 11. 



aa. Pectoral fins very large, wing-like, expanded at the base in front, this ex- 

 pansion being separated from the neck by a deep notch; no anal fin. 



Squatiuid^, 12. 



Family IV. SQUALIDJB. (The Dog-fishes.) 



Sharks with two dorsal fins, each armed with a stout spine, and 

 without anal fin ; no nictitating membrane ; spiracles moderate ; 

 gill openings narrow, all before pectorals ; ventral fins inserted 

 posteriorly ; teeth small, compressed ; nostrils inferior, near front 

 of snout. Genera 6 ; species about 15; small sharks, chiefly of the 

 Atlantic. {Spinacidm Auct.) 



a. Teeth in both jaws, simple, snbq\iadrate, each with a nearly horizontal 

 cutting edge, and a point directed outward; dorsal spines strong. 



Squalus, 5. 



5. SQUALUS (Artedi) Linnseus. 



7. S. acanthias L. Dog-fish. Dorsal spines not grooved; 

 slate-color, back with whitish spots fading with age. L. 3 feet. 

 North Atl., S. to Cuba ; abundant N., its liver valued for the 

 " Dog-fish oil." (Eu.) (Gr. aRavBias, having spines.) 



FAMiLy V. SOMNIOSID^. (The Sleeper Sharks.) 



Sharks with two dorsal fins, both without spine, and no anal fin, 

 the first dorsal much before ventrals, otherwise essentially as in 

 the SqualidcB. Genera 5 ; species 5 or 6, mostly large sharks of 

 the Atlantic. 



a. Dorsal fins about equal; upper teeth lancel>shaped, incurved; lower quad- 

 rate with a horizontal edge, ending in a point directed outwards; fins 

 very small Somkiosus, 6. 



6. SOMNIOSUS Le Sueur. (Lat., sleepy.) 



8. S. microcephalus (Bloch). Sleeper. Nurse. Color 

 blackish ; caudal blunt. L. 10 to 18 feet. Arctic seas, S. to Cape 

 Cod. (JSu.) (^jiLKpos, small ; Ke(f>a\ri, head.) 



Family VI. SPHTRNIDuSl. (The Hammer-Headed 

 Sharks.) 



Characters of the Galeorliinidce, except that the head has a form 

 hammer-shaped or kidney-shaped, its sides being much extended, 

 the eyes borne at the ends of the hammer. One genus, with 4 or 

 5 species ; large sharks of the warm seas. 



