Jordan and Ever matin. Fishes of North America. 53 



bb. Dorsal fins without spine, the first dorsal over or in advance of ventrals. 

 <. First dorsal much before ventrals; skin moderately rough. 



DALATIIDJE, xix. 

 a;. First dorsal opposite ventrals; skin with thorn-like tubercles. 



BcHiNORHimn*:, xx. 



Yi,! (reKrtav, a builder; crnov JvAo?, vertebra) : 

 mi. Vci (chni- with the calcareous lamella; ranged in several concentric series or rings about a 

 central axis ; pectoral fins very large, expanded horizontally and extended forward at 

 l>ase in front, giving the body the form of the flattened disk of the rays; the anterior 

 rxtensiui. separated from the neck by a deep notch, in which the gill openings lie ; no 

 anal I'm ; dorsal fins small, posterior; mouth broad, anterior. SQUATINIDA:, xxi. 



Suborder CYCLOSPONDYLI. 



Family XVIII. SQUALID^E. 



(THE DOG-FISHES.) 



Body more or less elongate. Head depressed. Eyes lateral, without 

 nictitating membrane. Mouth inferior, rather large, arched, a deep groove 

 on each side. Teeth compressed, variously formed. Nostrils inferior, 

 separate ; spiracles rather large ; gills openings moderate, all in front of 

 the pectoral fins. Dorsal fins 2, each armed with a spine ; the first dorsal 

 in front of the ventrals ; anal fin wanting ; caudal fin with the lower 

 lobe small or obsolete ; ventral fins inserted posteriorly, not much before 

 second dorsal. Oviparous. 



Genera 6 or more ; species about 15 ; rather small sharks, chiefly of the 

 Atlantic. These sharks represent a comparatively primitive type, appar- 

 ently not descended from any other existing Squali. (SPINACID.E, part, 

 Giinther, Cat., vm, 417-425.) 



a. Body rather elongate; no fold of skin along side of belly; dorsal spines both directed back- 

 ward. 

 b. Upper teeth simple, without smaller cusps at base. 



c. Teeth alike in both jaws, subquadrate, each with a nearly horizontal cutting edge 



and a point directed outward. SQUALUS, 37. 



cc. Teeth unequal, the upper very small, narrow, and lanceolate, erect, the lower more 

 or less oblique; dorsal spines hidden in the skin. CENTROSCYMNUS, 38. 



bb. Upper teeth each with 1 or '2 small cusps at base on each side. 



d. Teeth unequal, the upper erect and tricuspid, the lower oblique. ETMOPTERUS, 39. 

 dil Teeth equal, very small and pointed. CENTROSCYLLIUM, 40. 



37. SQUALUS, (Artedi), Linnaeus. 



Sqnnlii.*, (AnTEDi) LJNN^ITS, x, 1758, 233, (includes all sharks). 



$<iu<ili<s, TCAFINKSI.UE, Caratteri, etc., 13, 1810, (acanthias and uyalo; first restriction of the name 



St/iiahis, to species with spiracles and without anal fin). 

 Acanthorliinus, BLAINVILLE, Journal de Physique, 181G, 263, (acanthias). 

 Acaiitlrias, Risso, Europe Meridionale, in, 131, 1826, (acanlhias). 

 Fnto.ri/rlnnis, GILL, Proc. Ac. Nat. Sci. Phila., 1862, 496, (uyalo). 



Body rather slender. Mouth little arched, with a long, straight, deep, 

 oblique groove on each side ; no labial fold. Teeth rather small, all sim- 

 ple, equal in the two jaws, their points so much turned aside that the 

 inner margin forms the cutting edge. Spiracles rather wide, just behind 

 the eye. Fins moderately developed, the first dorsal larger than the sec- 

 ond, much in advance of the ventral fins, which are behind the middle of 



