20 Bulletin 47, United States National Museum. 



graclnally tai)ciing biickwaid; head liigb, with the forehead declivous, 

 little proiiiiueut; nostrils coulluent with mouth: mouth rather narrow, 

 the upper lip divided into 7 lobes, the lower with a fold; spiracles 

 small, below the lower part of the eye; no nictitating membrane; gill 

 openings rather narrow ; dentition similar in both jaws, small obtuse 

 teeth in front, which in the young are pointed, and provided with 3 to 

 5 cusps ; lateral teeth large, pad-like, twice as broad as long, arranged 

 in oblique series, one series being formed by much larger teeth than those 

 in other series; scales small, sometimes cruciform; caudal fin moderate, 

 more or less bent upward, and usually notched at tip. Oviparous, the egg 

 cases very large, subconical, without tentacles and spirally twisted. 

 Species about 4, all inhabiting the Pacific Ocean, usually placed in one 

 genus; 2 here recognized. Size small. (Cesthaciontid.k, Giiuther, Cat., 

 Vlii, 417-418; but Heterodontus, Blaiuville, 1816, has priority over 

 Cestkacion, Cuvier, 1817.) 



13. GYROPLEURODUS, Gill. 



Gyropleiuodns, Gill, Proc. Ac. Nat. Sci. Phlla., 1S62, 489, (fnincisci.) 

 Tropidodiis, Gill,?, c, {paHiherinus = quoyi). 



Branches of the lower jaw Avidely separated, the interval rounded in 

 front, growing wider behind. Molars in few rows; ridges above eye 

 prominent. Characters of the genus otherwise included above. Eastern 

 Pacific, (yipog, whorl; -KAe'vpov, side, bdovq, tooth.) 



a. Gill opouings uot very liigli, the length of tlie first slit being less tlian that of the branchial 

 region; molars in 4 to G rows; ridges above eye very prominent. 

 b. Molars convex, the larger ones not much if any carinated. francisci, 20. 



66. Molars carinate along their middle. Qi'Ovi, 21. 



20. GYROPLEURODUS FRANCISCI, (Girard). 

 (Bullhead Shark.) 



Head short and high, broad, but with subvertical sides ; the forehead 

 very declivous from eyes, the snout wide and transverse, but prominent ; 



2 blunt, diverging ridges continued from each side of the snout, ab- 

 ruptly merging into the more conspicuous superciliarj^ ridges, the in- 

 terval between which is nearly plane ; teeth in front digitated, with 



3 or 4 cusps, quiucuncially distributed in rows slightly converging 

 toward the middle; in the upper jaw, on the sides, molars oblong and 

 tlattoned, arranged in about 4 oblique whorls, uniform or increasing 

 backward, except the last, which is smallest; on the sides of the lower 

 jaw, also, are molars, oblong, with flattened crowns, and arranged in 

 transversely oblique whorls, but decreasing backward. Branches of the 

 lower jaw widely separated by an interval rounded in front and becom- 

 ing wider behind, the sides themselves being curved outward ; the acute 

 teeth confined to the front, the molar teeth few and disposed in about 



4 whorls, the first 3 of whicli slightly increase, while the fourth is almost 

 rudimentary. Branchial area almost oblong. Dorsal fins considerably 

 produced backward at their posterior angle; the compressed spine form- 

 ing about i of the base of each fin ; anal fin large, reaching the root 



