5. SPINACID^, 15 



teetli iinmerous, in two or more series, tlie point so much turned aside 

 tliat the inner margin forms a cutting edge, which is entire ; spiracles 

 moder-ate; no nictitating membrane ; gill-openings narrow ; fins all very 

 small, the ventrals nearly opjoosite the second dorsal; skin uniiormly 

 covered with minute tubercles. Species few, of the J^orthern Seas. 

 (Latin, somniosus, sleepy.) 



14. S. niicroceplisilus (Blocli) Gill. — Sleepei' Sharlc ; Nurse. 



Body robust, rapidly tapering behind; greatest depth about one- 

 fifth the length; head somewhat less; mouth moderate, upper jaw with 

 five rows of small sharp teeth, which are incurved and lancet-shaped ; 

 lower jaw with two rows of broad, quadrangular teeth, divided in their 

 centres by a perpendicular ridge and directed outwards, about 2G teeth 

 on each side; spiracles small; skin rough; fins small, the first dorsal 

 about as large as the ventrals and larger than the second dorsal ; pecto- 

 rals short; caudal short and bluutish. L. 8 to 20 feet (Storer). Cape 

 Cod to the Arctic Seas. 



(Sqnalus microccphnlus Blocli, Sclin. 135; Somniosus hrcvipinna Le Sueur, Journ. Ac. 

 Nat. Sei. Phila. i, 222; Scymnus hrcvipinna Storer, Fish Mass. 235; Lmmaryus horealis 

 Giiutlier, viii, 42G.) 



Family V.— SPINACID^. 



{The Dog-fishes.) 



Body more or less elongate; head depressed; eyes lateral, without 

 nictitating membrane ; mouth inferior, rather large, arched ; teetli com- 

 I^essed, variously formed ; nostrils inferior, lateral, near the front mar- 

 gin of the snout; spiracles moderate ; gill-openings moderate, ^ve on each 

 side, all in front of the pectoral fins ; dorsal fins tico, each armed with a 

 spine ; the first dorsal in front of the pectorals ; anal fin wanting; caudal 

 fin with the lower lobe small or obsolete; ventral fins inserted pos- 

 teriorly. 



Genera six or more ; species about fifteen ; rather small sharks, chiefly 

 of the Atlantic. (Spinacidce, part, Giinther, viii, 417-425.) 



* Tcotli equal in liotli jaws ; dorsal spines not concealed. 



a. Teetli very small, straight, jiointed, each with one or two smaller cusps on each 



side CeXTROSCYLLIUJI, 10. 



aa. Teeth moderate, simple, subquadrate, each with a nearly horizontal cutting 



edge, and a point directed outward Squalus, 11 . 



** Teeth unequal, those in the upper jaw erect, triangular, those in the lower jaw 

 more or less oblique ; dorsal spines hidden beneath the skin. Centkoscymnus, 12. 



