SQUALIDJE. — IV. 15 



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



Cakchakiid.k. 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 Lamxid.e, 10. 



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



teeth small (largest of all fishes) Cetorhixid.e, 11. 



an. 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 tin. 



VTIXID-E, 12. 



Family IV. SQTTALJD^, (The Dog-fishes.) 



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

 without anal fin; no nictitating memhrane ; spiracles moderate; 

 gill openings narrow, all hefore pectorals ; ventral fin< inserted 

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

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

 Atlantic. {Spinacidce Auct.) 



a. Teeth in both jaws, simple, subquadrate, each with a nearly horizontal 

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



Squalus, 5. 



5. SQUALUS (Artedi) Linnaeus. 



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

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

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

 " Dog-fish oil." (Tin.) (Gr. aKavSias, having spines.) 



Familv V. SOMNIOSIDuE. (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 Squalidce. Genera 5 ; species 5 or G, mostly large sharks of 

 the Atlantic. 



o. Dorsal fins about equal : upper teeth lancet-shaped, incurved; lower quad- 

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

 very small SoMOTOSUS, 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. (En-) (jiucpos, small; xcc^aXq, head.) 



Family VI. SPHYRNID^E- (The Hammer-Headed 



Sharks.) 



Characters of the Galeorkinidce, 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. 



