290 PLAGIOSTOMATA. 



Phil. Trans, lxviii, pt. ii, p. 786, pi. xii ; Pennant, Brit. Zool. (ed. 1776), iii, 

 p. 109 (ed. 1812), iii. p. 143. Be Bluet, Duhamel, Peches, p. 298, pi. xix, f. 6. 



Squalus glaucus, Linn, i, p. 401; Gmel. Linn. p. 1496; Bloch, Ich. iii, p. 712, 

 t. lxxxvi ; Bonnaterre, Ency. Ich. p. 9, pi. vii, f. 22 ; Lacepede, i, p. 213, pi. 

 ix, f . 1 ; Bl. Schn. p. 131 ; Turton, Brit. Fauna, p. 113 ; Risso, Ich. Nice, p. 26 ; 

 Bonaparte, Fauna Ital. Pesc. iii, p. 140, t. f. 2 ; Swainson, ii, p. 312. 



Carcharias glaucus, Cuv. Regne Anim. ; Flem. Brit. An. p. 167 ; Yarrell, Brit. 

 Fishes (ed. 1), ii, p. 381, c. fig. (ed. 2), ii, p. 498 ; Jenyns, Manual, p. 499 ; Gay, 

 Hist. Chile, Zool. ii, p. 364; White, Catal. p. 125; Thompson, Nat. Hist. 

 Ireland, iv, p. 250 ; Giinther, Catal. viii, p. 364 ; Giglioli, Catal. Pesc. Ital. p. 51 ; 

 Moreau, Poiss. de la France, i, p. 329, fig. 50. 



Squalus (Carcharinus) cmruleus et glaucus, Blainv. Fauna, Fr. i, pp. 90-92, 

 pi. xxiii ; Gray, Cart. Fish. p. 44. 



Carcharias (Prionodon) glaucus, Mull, and Henle, p. 36, pi. xi ; Yarrell, 1. c. 

 (ed. 3) ii, p. 482, c. fig. ; Dumeril, Ich. i, p. 353. 



Carcharias (Prionodon) hirundinaceus, Dumeril, 1. c. p. 354. 



Blue shark, Couch, Fish. Brit. Isles, i, p. 28, pi. vi. 



Form elongated. Snout longitudinally produced and covered with numerous 

 fine punctures. Eyes — midway between the end of the snout and the anterior 

 gill -opening. Cleft of mouth deep, its gape wide ; no labial fold at the angle of 

 the mouth. Nostrils transverse, plrced midway between the front edge of the 

 eye and the end of the snout, or rather nearer the month. Teeth — in four or five 

 rows, and altering with age. In the very young the edges are smooth, while the 

 teeth in both jaws are oblique and not swollen at their bases. Next a few 

 denticulations appear at their bases, when, from 4 to 6 feet long, the whole teeth 

 are serrated ; but in old examples these serrations become obsolete, and the 

 teeth in the lower jaw are narrow, and either stand obliquely or erect upon a 

 broad base. Fins — two dorsals : the first somewhat quadrangular, placed in 

 about the centre of the distance between the snout and the base of the caudal, 

 and in about the centre of the interspace between the pectoral and the ventral ; 

 second dorsal about half the size of the first and placed above the anal, half the 

 distance nearer the candal than the first dorsal. Pectoral large and falciform, 

 reaching to beneath the first dorsal. Ventrals small. Caudal with a notch or pit 

 at its base, its length equalling about one-fourth of the total, its lower lobe short, 

 and the lower surface of its upper lobe notched near its extremity. Skin 

 moderately rough. Colours — back and upper half of body of a deep blue, sides 

 and abdomen white : snout sea-green, fins dark, pectoral nearly black. 



Names. — Blue shark, from its colour. Morghi glas, y Bierc, Welsh. Be Bleu, 

 French. 



Habits. — A migratory and voracious form being found off our shores mostly 

 during the warm months of the year, at which time should it be calm and warm 

 they come to the surface in the daytime, and move gently along with the end of 

 the tail and tip of the dorsal fin out of the water (Dunn). Although Couch had 

 known one in Cornwall as early as the first week in March, it is not generally present 

 before June. It is but rarely seen off our shores of sufficient size to be dangerous 

 to man. It is said to have a great affection for its young, and it has even been 

 asserted that in times of danger they enter its mouth and seek refuge in its 

 stomach. " When in pursuit of prey or excited, they continually cover and 

 uncover their eyes with their nictitating membrane. The time of their greatest 

 activity is at night, when they may be seen stealing through our summer seas 

 like beasts of prey : their bodies not even disturbing the phosphorescence which 

 at that time of the year so fills the ocean. A most puzzling circumstance ; and 

 but for the flexible part of the dorsal fin and tip of the tail, it would be impossible 

 to detect their presence in the darkest night" (Dunn). It feeds on sardines, 

 herrings, mackerel, even tearing them out of the nets. Couch has removed from 

 the stomach of one, which measured 6 feet in length, a large picked dog-fish and 

 a conger, each bitten across the middle, also a gray gurnard. They are tenacious 

 of life, and Couch instances one which, having been thrown into the sea after 

 its liver had been removed, pursued and tried to secure a mackerel. 



