ISISTIUS BRASILIENSIS. 39 



directly forward from the suboi-bital for some distance, then cnrves out 

 and upward to connect with the rostral above the nostril. All the 

 sections of the tube, or tubes, present on Isiinis pimctatns, as on the 

 figure shown in the '• Lateral System," Plates I. & X., in Mem. Mus. 

 Comp. Zoijl., XVIL, are represented on Isistius, the short orbitonasal 

 excepted. 



There is more reseml)lance between these greatly differentiated genera 

 in the lateral sj'stems than in most other respects. Outside of the Scym- 

 norhinidte the closest affinities, as indicated by the lateral systems, are 

 to be seen in the spinacoids; this will be sufficiently demonstrated by 

 comparison with Centroscyllium, Plate LXIX., fig. 1. 



The individual described represents the most common type of color- 

 ation ; it is chestnut brown, darker on the back, and on the hinder j^ortions 

 of the caudal lobes. The hind borders of the fins, excepting the border 

 of the upper lobe of the caudal, are light. Commonly a dark band crosses 

 the throat ; it does not show on specimens of very dark color. In life 

 a remarkable feature of this shark is its pho.sphorescence. The peculiarity 

 is well described by F. D. Bennett, 1840, from living examples. " The 

 entire inferior surface of the body and head emitted a vivid and greenish 

 phosphorescent gleam, imparting to the creature, by its own light, a 

 truly ghastly and terrific appearance. The luminous effect was constant, 

 and not perceptibly increased by agitation or friction. . . . The only 

 part of the under surface of the animal which was free from luminosity 

 was the black collar around the throat ; and while the inferior surface of 

 the pectoral, anal, and caudal fins shone with splendour, their superior 

 surface (including the upper lobe of the tail-fin) was in darkness, as also 

 were the dorsal fins, back and summit of the head." The luminous gleam 

 was constant during the life of the captive, but declined and vanished 

 when the shark died. G. Bennett, 18G0, describes another specimen. " On 

 placing my fish in sea-water and observing it in a dark cabin, it swam about 

 for some time, emitting a brilliant phosphoric light; and when this had 

 become so faint as to be almost imperceptible, it was readily rekindled 

 on the animal being disturbed or excited. My specimen was of a perfectly 

 black colour, and died about four hours after it had been taken. The 

 luminosity was retained for some hours after life was extinct." These 

 observations were confirmed by those of Professor A. Agassiz on the speci- 

 men here described. 



