420 FISHES. 



mudferous cavities lahich are covered with a thin skin. Ven- 

 tral fins thoracic, ivith one spine and more than five soft rays 

 {in Monocentris witli fv:o only). 



One family only belongs to this division. 



Family — Beiiycid.e. 



Body short, icith ctenoid scales, ichich arc rarely ahscnt. 

 Eyes lateral, large {except Melamphaes). Cleft of the mouth 

 lateral, ohlicjue ; jravs vnth rilliform teeth ; prdate genercdly 

 toothed. Ojxrcnlar hones more or less armed. Eight {four) 

 hrancliiostcgcds. 



Tins family offers several points of biological interest. 

 All its members are strictly marine ; but only two of the 

 genera are surface-forms {Holocentrum and Myripristis). All 

 the others descend considerably below the surface, and even 

 some of the species of Myripristis habitually inhabit depths 

 of from 50 to 100 fathoms, Polymixia and Beryx have been 

 found in 345 fathoms. Melamp)haes must live at a still greater 

 depth, as we may infer from the small size of its eye ; this 

 fish is not likely to come nearer to the surface than to about 

 200 fathoms. The other genera named have extremely large 

 eyes, and, therefore, may be assumed to ascend into such 

 superficial strata as are still lit up l)y a certain proportion 

 of sun-rays. The highly-developed apparatus for the secre- 

 tion of superficial mucus, with which these fishes are provided, 

 is another sign of their living at a greater depth than any of 

 the preceding families of Acanthopterygians. In accordance 

 with this vertical distribution, Berycoid fishes have a wide 

 horizontal range, and several species occur at Madeira as Avell 

 as in Japan. 



Fossil Berycoids show a still greater di^^ersity of form 

 than living ; they belong to the oldest Teleosteous fishes, the 

 majority of the Acanthopterygians found in the chalk Ijeing 

 representatives of this family. Beryx has been found in 



i 



