DEEP-SEA FISHES. 299 



The Gadidae, Ophidiidas, Macruridaa, and Scopelidos make up a 

 very large proportion of the deep-sea fauna, which has thus far 

 yielded some ninety to one hundred or more genera. The eels 

 (Muraenidse) are largely represented, and have been dredged from 

 depths extending to 2,500 fathoms. Very few cartilaginous fishes 

 were obtained by the ''Challenger," and these (Scyllium, Centro- 

 phorus, Raja) were restricted to water not much exceeding six hun- 

 dred fathoms, although the same group of fishes yielded specimens 

 to the "Talisman" at nearly twice this depth (coast of Portugal). 



Whether or not different zones of ichthyic life can be recognised 

 in the oceanic abyss may perhaps still be considered an open ques- 

 tion. Dr. Gunther maintains, as the result of his studies, that "as 

 far as the observations go at present, no distinct bathymetrical 

 regions which would be characterised by peculiar forms can be 

 defined," and that, "if the vertical range of deep-sea fishes is 

 actually as it appears from the ' Challenger ' lists, then there is no 

 more distinct vertical than horizontal distribution of deep-sea 

 fishes." As a result of the explorations of the "Talisman," Filhol 

 arrives at the opposite conclusion, and believes that a series of 

 more or less distinct zones can be indicated. Although in its gen- 

 eral features the abyssal fauna ("Bassalian" of Gill) is closely 

 related to that of the superficial tracts, yet a number of distinctive 

 elements, arising in part from certain remarkable abnormalities of 

 structure, or from the presence of types not elsewhere represented, 

 serve in a measure to define it. Professor Gill indicates twenty- 

 eight families of deep-loving fishes. 113 



Of the two lowest orders of fishes, the Pharyngobranchii, as rep- 

 resented by the Amphioxus or lancelet, and the Marsipobranchii, 

 lampreys and hags, no unequivocal fossil remains have as yet been 

 discovered. Possibly, however, some of the singular tooth-like 

 bodies described as conodonts from the Cambrian and Silurian de- 

 posits, which by many authors are referred to the dental armature 

 of annelids, may belong to fishes more or less nearly related to the 

 modern hag. 



The Elasmobranchii (sharks, rays) have their oldest representa- 

 tives in the Upper Ludlow horizon of the Upper Silurian formation, 

 being preceded in time by a bucklered ganoid, Pteraspis (Scaphas- 

 pis) Ludensis, from the Lower Ludlow. These earliest remains, 

 belonging to the family of the true sharks (Squalidse), are in the 



