364 DEEP SEA FISHES. 
Macrurus canus and Halosaurus radiatus, Plate LXXXI1V., exemplify very 
diverse forms, dwelling at the bottom, secured from moderate depths. 
Compared with MW anguliceps, M. canus, from 210 fathoms, has a larger eye 
and a somewhat smaller degree of development in the disks of the oral series, 
and the frontal disks are quite as well developed as any of the others. 
This species is an intermediate between Macrurus and Trachyrhynchus ; 
there are 68 cephalic disks. On Halosaurus the relative positions of the 
disks (which are no doubt lanterns and flash lights) and the eyes are much 
like that of a dark lantern and an observer who keeps himself out of sight 
in the shadow while throwing the light upon objects around him. On some 
species the disks are covered by screens which prevent escape of the light 
in other directions than downward away from the body. On the upper sur- 
faces of the head the disks are comparatively few, are much less developed, 
and are not apparent in the cranials backward of the orbital branches. 
Backward of this point the cranials and the aural branches, which latter 
unite on the occiput, are hard-walled tubes and much more primitive in char- 
acter; but on the body the greatly differentiated disks reappear, closely 
underlaid by the especially large branch of the vagus by which they are 
innervated. In the figures this nerve would appear to be forward of the 
pectorals; in reality it passes above and down immediately behind them. 
