NATURAL SCIENCES OF PHILADELPHIA. 487 



Dorsal Distance from snout 30 ; length of base 10 ; length of horizontal 

 ''posterior" margin 4J; greatest oblique height 9; (second) distance from 

 snout 58 ; length of base 8 ; length of posterior (horizontal) margin 3 ; greatest 

 (oblique) height 7. 



Anal Distance from snout 61 ; length of base 6 ; greatest height 4 ; height 

 behind to point 3j. 



Caudal Length 23 ; length of inferior lobe 15; oblique height of lobe near 

 front 5 ; oblique height at end 1 J ; greatest height of terminal lobe 3j. 



Pectoral Greatest length 12J; length within internal border 9 ; greatest 

 width 8. 



Ventral Distance from snout 33 ; greatest length (from base to inside of outer 

 angle) 5| ; length within internal border 4 ; greatest width ts. 



Genus TRIACIS Muller and Henle. 



Triakis Muller et Henle, Magazine of Natural History, vol. ii. 1838. 



" Bonaparte, Selachorum Tabula Analytica, 1838. 



" Midler et Henle, Systematische Bescbreibung de Plagiostomen. 



" Girard, Explorations and Surveys for a Railroad Route, &c, vol. x. 

 Fishes, p. 362. 



Body compressed, elongated and scarcely subfusiform in profile. 



Scales provided with three keels producing a tridigitate margin. 



Head scarcely oblong, with the snout short and transverse, the anterior mar- 

 gin being arched or convex. 



Eyes rather small, and nearly above the angles of the mouth. 



Mouth large and transversely arched. The groove at each corner of the 

 mouth is very sharply defined, and the upper lip folds over the angle of the 

 lower. 



Teeth with a large acute median prong, and two smaller oblique ones on 

 each side ; the unpaired symphiseal tooth is symmetrical. 



Nostrils nearer the mouth than the front of the snout, transverse and with a 

 wide convex flap arising from the anterior (inner) border. 



Dorsal fins similar in form, obliquely produced towards the anterior angle 

 which is rounded; acutely elongated from the posterior angle ; the first fin is 

 rather nearer the ventrals than the pectorals ; the second is smaller and partly 

 in advance of anal. 



Anal fin similar to second dorsal. 



Caudal fin with a terminal triangular lobe, and with the membrane above the 

 vertebral column moderately developed; inferior lobe obsolete or scarcely pro- 

 duced downwards and obtuse. 



Pectoral fin rather small, rounded at each angle, not extending beyond the 

 front margin of first dorsal. 



Ventral fins trapezoidal, rounded at the external angle. 



Type. Triacis scyllium M. and H. 



Two species of this genus are known ; Triacis semifasciatus Girard, from 

 California ; Triacis scyllium Muller and Henle from Japan. 



Triacis semifasciatus Girard.* 

 Triakis semifasciatus Girard, Proc. Academy of Natural Sciences of Phila., vol. 



vii. p. 196, 1854. 

 Mustelus felis Ayres, Proc. California Academy of Natural Sciences, part 1, p. 



17, 1854. 



* Ihe following name probably belongs to the synonymy of Triacis semifasciatus, but as it ha3 

 never been joined to a description, the suggestion can be only verified by one having access to the 

 British Museum. It is scarcely necessary to add that such a verification will not at all influence 

 the nomenclature of the species, the name being a worthless synonym by default of description. 



Triakis californica Gray, List of Specimens of Fish, in the Collection of the British Museum, 

 part 1, Chondropterygii, p. 56, 1851. 



1862.] 



