36 DEEP SEA FISHES. 



.above the hindmost tooth in the latter, or over the junction of the hibials, 

 the outer end of the upper jaw appears as a short horizontal bar. Above 

 the end of the upper jaw and forward of the inward process of the lower, 

 fig. 4, there is a small subquadrangular spiracular cartilage. Behind each 

 half of the lower jaw, in fig. 4, Plate II., behind the end of the broadened 

 lower labial, there is an unnamed subcrescentic, very thin, apron-like 

 cartilage, strongly invested in ligamentary tissue, underlying the ends of 

 ceratohyal and basihyal. Rudiments of these cartilages are to be seen in 

 the same positions on Scymnorhinus licha, where apparently they are in 

 process of acquisition. 



The basihyal is wide and strong, and is deeply excavated on its lower 

 surface for the ends of the ceratohyals, which it overlaps considerably. Be- 

 hind this arch the branchihyal skeleton is decidedly feeble, Plate II., figs. 6, 

 7. In the specimen at hand the basibranchials appear to be obsolete, unless, 

 perhaps, exception is to be made for a couple of short longitudinal bars of 

 cartilage lying between the ends of the hindmost branchihyals but not in 

 contact with them. The lower ends of the ceratobranchials taper to points 

 that are neither in contact with one another nor with the basihyal; the an- 

 terior ceratobranchial is short and does not extend down as far as either of 

 the others. Below the ceratobranchials the extrabrauchials form an irregu- 

 lar sheet of cartilage as thin as paper, Plate II., fig. 6. In figure 7 a dorsal 

 view of the branchial skeleton of the right side is given, the forward por- 

 tion being turned to the left. The segmentation of the second and third 

 pharyngobranchials in this figure is no doubt accidental, as also is the divi- 

 sion between the hindmost two of the arches, where the epibranchials should 

 be so united with and by the pharyngobranchials as to be a continuous 

 cartilage. 



A specimen of Scymnorhinus licha dissected for comparison with Isistius 

 differs slightly from that figured by Gegenbaur, especially in regard to the 

 branchial cartilages. It has three distinct basibranchials behind the basi- 

 hyal, the second of which is like the first in shape and attachments and in 

 being without the division near the middle as seen in the mentioned figure 

 (Das Kopfskelet, Plate XIX., fig. 2). In this specimen the pair of basihyals 

 immediately in front of the hindmost basibranchial are in contact on the 

 median line and separate that basibranchial from the one next in front of it- 

 There is, in fact, no trace of the small median plate marked " C "' " in Ge- 

 genbaur's figure. 



