REPORT ON THE DEEP-SEA FISHES. 247 



the entire front part of the palatal arch can be moved in a vertical direction, thus 

 assuming the function of the immovable upper jaw. 



The mandible is short and deep, with a very thin rudiment of Meckehan cai'tilage ; 

 only a dentary and articulaiy can be distinguished. 



The prseoperculum (fig. 9, pr) consists of a narrow vertical, and similar horizontal 

 limb, both meeting at a right angle. The operculum (o) is membranous, rayed, frayed 

 on the edge ; the suboperculum (so) of similar structure, narrow ; the interoperculum 

 (io) smooth and firmer, attached to the lower limb of the prasoperculum. 



Infraorbital bones are absent. 



The hyoid and branchial arches do not oS'er any noteworthy peculiarity, except that 

 the nine slender branchiostegals are crowded together on the epihyal and the 

 cartilaginous end of the ceratohyal, being enclosed in the same membrane as the 

 operculum and suboperculum. 



The scapulary arch (fig. 10) is very simple, and suspended from the cranium by 

 loose and easUy detached ligaments. The clavicle (cl) is narrow and curved, the single 

 supracla-^dcle (scl) not much smaller and single. As usual a urohyal (tih) is attached to 

 the symphysis of the clavicle. The scapula (sc) and coracoid (co) form an extremely 

 thin lamina, of which a great portion remains cartilaginous. Basalia minute. Post- 

 clavicle absent. 



The centra of the vertebvce are deeply biconcave, perforated in the middle, rather 

 short and broad, with deeply pitted outer surface, the abdominal surface of those of the 

 trunk being remarkably flat. The caudal vertebriB, whUst retaining their short longi- 

 tudinal axis, are more and more compressed towards the end of the tail, and those of 

 the extremity of the vertebral column are more elongate, and finally become quite 

 rudimentary. 



The articulation of the first vertebra with the skull is not effected merely by a 

 simple circular concavity, but there is a distinct median osseous projection on the 

 upper margin of the centrum of the vertebra, whilst the opposite part on its lower 

 margin recedes further backwards than the lateral portions of the joint. 



There are forty-two vertebrae in front of the one which supports the first 

 interneural, and forty-nine may be reckoned as belonging to the abdominal portion of 

 the column. 



The neural arches of the abdominal vertebroe are broad and solid, terminating in 

 short and much depressed neural spines. Posteriorly the neural spines become longer, 

 slender, needle-shaped, and disappear on the rudimentary vertebrae at the extremity 

 of the column. 



The interneural spines are broad lamella?, which assume a very oblique position, 

 each being provided with a strong longitudinal ridge, at the top of which the dorsal 

 spine is joined. 



