ISISTIUS BRASILIENSIS. 39 
directly forward from the suborbital for some distance, then curves out 
and upward to connect with the rostral above the nostril. All the 
sections of the tube, or tubes, present on Jswrus punctatus, as on the 
figure shown in the “Lateral System,” Plates I. & X., in Mem. Mus. 
Comp. Zodél., XVII., are represented on Isistius, the short orbitonasal 
excepted, 
There is more resemblance between these greatly differentiated genera 
in the lateral systems than in most other respects. Outside of the Scym- 
norhinide 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 portions 
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 phosphorescence. 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, 1860, 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. 
