18981 THE ANTIQ UITY OF DEEP-SEA FISH-FA UNA 259 



Cretaceous are also probably somewhat allied to the strange eel- 

 shaped fishes of the family Halosauridae, which are a characteristic 

 feature of the surviving deep-sea fish-fauna. These fishes have a 

 very long tapering tail, with no separate caudal fin, but their dorsal 

 fin is short in the middle of the back, and both the pectoral and 

 pelvic paired fins are present. The body is covered with scales, 

 and those of the lateral line, displaced close to the ventral border, 

 are enlarged to bear a series of luminous organs. It is interesting 

 to note that these unique fishes have also been identified quite 

 lately (^) in the Cretaceous of Westphalia ; the so-called Echidno- 

 cSphalus of the latter formation being essentially identical with the 

 siirviving Halosaurus, and displaying even the enlarged series of 

 scales observed in the latter. 



As to the fishes most closely related to Flops and the herrings, 

 there are not many in Cretaceous deposits which can be claimed as 

 truly deep-sea forms. Of these, indeed, there is only one of much 

 importance — Istiens from Westphalia (*) and the Lebanon Q-) ; but 

 this genus is of the greatest interest, because there are no means at 

 present of distinguishing it from the surviving Bathythrissa of the 

 deep sea near Japan. The latter fish is known only by two speci- 

 mens, one in the British Museum, the other in the Berlin Museum, 

 which can hardly be dissected ; and the fossil form, which is abun- 

 dantly represented in Westphalia, is thus destined to afford the first 

 information concerning the skeleton. It is a fish much like Flops 

 in general character, but the dorsal fin is considerably extended 

 and fringes the greater part of the back. 



With regard to the Berycoids of the Cretaceous, there is nothing 

 worthy of remark, except that very few of the so-called Beryx truly 

 belong to that existing genus. As at the present day, some genera 

 have the aspect of deep-sea forms, while others are as clearly adapted 

 for a shallow-water or surface habitat. 



The most striking difference between the deep-sea fish-fauna of 

 the Cretaceous period and that of the existing ocean consists, indeed, 

 in the preponderance of physostomous species in the former and in 

 the complete absence of eels and the Anacanthini — the cod-fishes 

 and their allies. At the present day, according to Dr Glinther, the 

 species of Scopeloids form about one quarter of the total fauna, while 

 the Anacanthini constitute another quarter, and the strange forms of 

 eels are an important element. In the Cretaceous fauna, it is 

 scarcely too much to say that (so far as known) the Scopeloids 

 comprise half the species, the other Physostomous fishes at least 

 another quarter, and the Berycoids and their allies the remainder. 

 The only traces of eels hitherto discovered in the Cretaceous are 

 a few specimens of quite normal shallow-water types in the 

 Lebanon (^) ; and no fishes of this remote date from any part of the 



