Fishes of the Western North Atlantic 233 



Mus. nat. Hist., 7^, 1937: 41, 119 (class.) ; Fowler, Bull. U.S. nat. Mus., 100 {13), 1941 : 1 18 (part, 

 class.). 



Family TRIAKIDAE 

 Smooth Dogfishes 



Characters. Two dorsal fins, the ist much shorter than the caudal, its base terminating 

 anterior to origin of pelvics; caudal less than ^4 of total length, not lunate, its lower ante- 

 rior corner expanded as a low lobe only, if at allj caudal peduncle not flattened dorso- 

 ventrally or expanded laterally, with or without a precaudal pit above, but none below j 

 sides of trunk, anterior to anal, without longitudinal ridges; inner margins of pelvics en- 

 tirely separate posterior to cloaca in both sexes; snout not greatly elongate, or jaws widely 

 protrusible; 5th gill opening posterior to origin of pectoral; gill arches without rakers and 

 not interconnected by a sieve of modified denticles; nostril either separate from mouth or 

 connected with latter by a groove, its anterior margin without barbel; spiracles present 

 or absent; lower eyelid with a longitudinal fold externally, but without internal nictitating 

 membrane; jaws with or without labial furrows; teeth small, rounded, or with 3 to 4 

 distinct cusps; several series functional along entire length of jaw; dermal denticles ovate, 

 lanceolate or tridentate; head of normal shape and not widely expanded laterally. Rostral 

 cartilages 3, united terminally; most of the radials of pectoral on metapterygium ; meso- 

 and propterygia much smaller; meso- and metapterygia separated by a foramen, at least in 

 some cases; heart valves in 3 rows. Development either ovoviviparous, or viviparous with 

 a well developed yolk-sac placenta. 



Genera. These small sharks, of shoal or moderate depths, are widely distributed in 

 tropical and warm temperate belts of all oceans. They are perfectly harmless. The group 

 is very close to the Carcharhinidae where it is placed as a subfamily by Fowler,^ although 

 it more resembles the Orectolobidae and the Scyliorhinidae in its dentition. However, 

 the triakids seem sufiiciently different both from the typical carcharhinids (with respect 

 to the teeth and the absence of a true nictitating membrane), as well as from the orectolo- 

 bids and scyliorhinids, to be ranked as a distinct family for convenience, if for no better 

 reason. 



The family, as defined above, corresponds to the Galeorhinidae as used by Garman 

 and by many subsequent authors. But the latter name is not appropriate in the present 

 connection, because Galeorhinus Blainville, 1 8 1 6, from which it is derived, is the correct 

 name of the so-called "Topes," a genus of carcharhinid sharks (see footnote 4, p. 264), 

 and not of the Smooth Dogfishes (Muslelus) to which Garman" and others have ap- 

 plied it. For this reason Bigelow and Schroeder^ substituted Mustelidae for the sharks 

 now in question, overlooking the fact that this name had been in common use for a family 



I. Bull. U.S. nat. Mus., 100 (75), 1941 : i 27. 2. Mem. Harv. Mus. comp. Zool., 3d, 191 3 : 3, 169. 



J. Canad. Atlant. Fauna, biol. Bd. Canad., 12^, 1934: 6. 



