202 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



cell plates of the cephalic discs of //. radudns. In II. macrochir the upper 

 ends of these cells are strongly curved and pass into a superficial pellicle 

 which looks as if it were composed of the upper ends of the cells them- 

 selves, drawn out in a thread-like fashion and laid down tangentially. 



Macrurus canus Garmau. 



Plate 5, Figs. 18-30. 



This species has been described by Garman ('99, pp. 217, 364, Plates 49, 

 84, Figs. 1, 2). The radiating discs are situated in the floors of the cephalic 

 slime canals. In surface views they appear elongate hexagonal (Plate 5, 

 Figs. 19, 20). They are 2-4 mm. long, white in color and very conspicu- 

 ous. The wall of the slime canal is lustrous and the part surrounding the 

 discs occupied by large and richly ramified dark brown pigment cells (Figs. 

 19, 20 p) so that they stand out as brilliantly white patches from a dark sur- 

 rounding. On each side of the head there are 3 maxillary, G orbital, 2 eth- 

 moidal, 16 occipitoparietal, 7 mandibular, and 6 opercular radiating discs. 

 A stout nerve, the main disc nerve, (Plate 5, Figs. 19, 20 n) approaches each 

 of these organs from the side and extends through its basal part towards its 

 centre, where it abruptly divides into numerous paratangentially extending 

 branches. These discs are exceedingly tender structures, and unfortunately 

 not sufficiently well preserved to allow of their minute structure being 

 clearly made out. A square patch occupying the central part of tlie hex- 

 agonal disc is much less transparent than the remainder (Figs. 19, 20), and 

 it seems that the ramifications of the main disc nerve are confined to this. 

 The discs here are certainly not so simple in structure as in Leucicorus and 

 Bassozetus and seem to approach those of Halosaurus. They probalily have 

 a structure similar to that of Halosaurus. 



Ipnops agassizii Gaiman. 



Plate 1, Figs. 3-5. 



This species was described by Garman ('99, p. 259, Plate H, Figs. 2, 

 2 a). On the upper side of its dorso-ventrally compressed head a whitish 

 patch 12 mm. long and e(iually broad, composed of two symmetrical halves, 

 a right and a left one, is met with (Plate 1, Figs. 3-5 d). Moseley ('87, pp. 269- 

 27G, Plates 67, 08) has found similar discs in another species of this genus. 



