362 DEEP SEA FISHES. 
placed so as to bring their functional field most completely within the field 
of vision, a fact which strongly supports the theory of luminous disks on 
certain species. Those disks out of the visual field, or better those function- 
ing toward points not reached at the same instant by the eye are less devel- 
oped. Thus it happens that the disks on the forward portion of the snout 
and those back of the head at the angle of the gill opening are smaller than 
those nearer the eye, while, being in better position, they are larger than 
those below the lower jaws. Similar statements may be made concerning 
the species of Eretmichthys. On the head of B. nasus there are 58 disks. 
Evetmichthys pinnatus and EF. ocella, Plate LXXIX., resemble Lassozetus 
nasus in regard to differences in the developement of the disks on different 
parts of the head; neither of them has frontal branches and each has two 
disks in each aural branch. These forms are readily separated by details 
of the system, though the pectoral oars of EH. pinnatus and the pores on the 
head of #. ocella render it hardly necessary to go below the surface for aid. 
E. pinnatus has 54 cephalic disks and /. ocella has 56. 
Bassogigas stelliferoides and Catetyx simus, Plate LXXX., belong to very 
distinct genera. The most prominent differences in the systems, besides 
that in the number of disks, are perhaps those due to the elongation and 
the depression of the head in Catswtyx: the disks are far apart in the 
longitudinal canals and close together in the vertical, that is, in the post- 
orbital and the spiracular. In both species the disks are comparatively 
small and are of nearly uniform size on all parts of the head; both are 
without frontal branches, ZB. stedliferoides has 64 cephalic disks, two of them 
in each aural branch, and (. simus has 50 disks on the head, but one of 
which appears in each aural. 
Lamprogrammus illustris and Phycis regius, Plate LXXXI., present differ- 
ences of the most marked character. The disks of the first are large but 
very slender aud spindle-shaped; the series are complete; and, a feature 
not yet noted on others, the frontal branches have joined the aurals forming 
a complete loop, which, however, contains but three disks, the one ordi- 
narily found in each frontal branch and the two most often occurring in each 
aural. There are 56 cephalic disks; those of the body are similar to those 
of the head. On Phycis regius the disks about the eyes are the better 
developed ; those on the aural region are rudimentary and obsolescent, 
their places being occupied by a cavity of some size, filled with a gelatinous 
mass and mucus, into which canals are carried as hard-walled tubes, one 
