SQUALUS.] PISCES (CARTILAG.) PLAGIOSTOMI. 499 



the remaining portion free. (Colours.) Bluish gray above, white be- 

 neath; the pectoral fins attached to the white portion." BLAINV. 



Met with occasionally on the British coast, but not very plentiful. 

 Derives its English name of Thresher from its supposed habit of attack- 

 ing and striking the Grampus with its long fox-like tail *. 



188. S. glaucus, Linn. (Blue Shark.) Teeth in 

 the upper jaw triangular, and curved; in the lower jaw 

 longer, and more straight ; all denticulated : body slender, 

 slate-blue above. 



S. glaucus, Linn. Syst. Nat. torn. i. p. 401. Watson in Phil. Trans. 

 (1778.) vol. LXVIII. p. 789. pi. 12. Block, Ichth. pi. 86. S. cseruleus, 

 Blainv. Faun. Franc, p. 90. Galeus glaucus, Witt. Hist. Pise. 

 p. 49. Carcharias glaucus, Flem. Brit. An. p. 167. Blue Shark, 

 Penn. Brit. Zool. vol. in. p. 109. Id. (Edit. 1812.) vol. HI. p. 143. 

 Le Bleu, Cuv. Reg. An. torn. n. p. 388. 



LENGTH. Six or seven feet. PENN. (Edit. 1812.) 



DESCRIPT. (Form.) Elongated: the skin less rough than in the 

 others of this genus : snout long, sharp, depressed, not pellucid at the 

 extremity, punctured above and below with numerous pores: (mouth 

 large, widely cleft ; teeth numerous, in four or five rows ; the upper ones 

 broadest, curving a little backwards, and denticulated at the edges ; the 

 lower ones narrower, straight, in the form of a scalene triangle, and finely 

 denticulated :) nostrils long, transverse, (equally distant from the edge of 

 the jaw, and the extremity of the snout:) eyes elliptic, but the irides 

 exactly circular, the pupils lenticular and transverse ; (commissure of the 

 lips extending far beyond them:) no temporal orifices: five branchial 

 openings, (moderate, elevated, lateral ; the first three largest and furthest 

 asunder ; the last two, especially the fifth, smaller, and closer together :) 

 two dorsals ; the first at about the middle of the length, excluding caudal ; 

 (triangular, of moderate size, the base longer than the two other sides :) 

 second dorsal not far from the setting on of the caudal, (much smaller, 

 equally triangular, and much more inclined :) anal answering to this last 

 fin : tail (scarcely equalling half the body,) with a triangular excavation 

 at the upper part of the base of the caudal fin ; this last with two lobes, 

 the upper extending very far beyond the lower, and terminating in an 

 acute angle : vent at the distance of more than one-third of the length 

 from the setting on of the caudal : pectorals large, (falciform,) very long, 

 terminating in an acute angle: ventrals small, (cut square behind.) 

 (Colours.) Back of a fine, moderately deep, blue: belly silvery. WILL. 

 and BLAINV. 



Said to be not uncommon on some parts of the coast, particularly that 

 of Cornwall during the pilchard season. The specimen described by 

 Dr. Watson in the "Philosophical Transactions" was taken on the coast 

 of Devonshire. It is possible, however, that in the case of this species, 

 as in that of the S. Carcharias, two or more have been confounded 

 under one name. The above description is from Willughby, and is that 

 of a specimen observed by him at Penzance. It appears to be the same 

 as the S. cceruleus of Blainville, from whom I have borrowed some addi- 

 tional characters t. The /S. glaucus of this last author is a closely allied 

 species, in which the teeth are not denticulated at the sides. 



* Borl. Cornw. p. 265. 



t The parts borrowed from Blainville are included in parenthesis. 

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