258 NATURAL SCIENCE . [April 



Cretaceous times, and have descended more recently. Among fishes, 

 however, it is usually possible to distinguish the deep-water forms 

 by their comparatively delicate skeleton, or by their attenuated fin- 

 rays, or by indications of a great development of the slime-canal 

 system which is related to the production of luminosity or even to 

 the formation of special luminous organs. Judged by these criteria, 

 the majority of the deep-sea fishes of the Cretaceous period are more 

 or less closely related to the Scopeloids and Berycoids, which still 

 form so conspicuous an element in the abyssal fauna. They are 

 best known thus far from the Chalk of England, and from 

 equivalent deposits in Westphalia {^), Bohemia, Dalmatia, and 

 the Lebanon (^). 



Some of the Cretaceous Scopeloids with a delicate skeleton — such 

 as the so-called Sardinius and Sardinioides from Westphalia (*) — 

 can scarcely be distinguished from existing deep-sea members of the 

 family Scopelidae. Others, however, clearly belong to extinct groups, 

 and among the latter may be particularly mentioned the long and 

 slender fishes of the family Dercetidae or Hoplopleuridae. The 

 little arrow-head-shaped, spiny scutes of Dercetis are common in the 

 English Chalk, and nearly complete skeletons of the fishes to which 

 they belong are found both in Westphalia and the Lebanon (^). The 

 head and trunk are almost eel-shaped, but the skin is armoured with 

 longitudinal series of the small spiny scutes. Both pairs of fins are 

 present ; and the median fins are divided into three, namely, one 

 comparatively extensive dorsal, a slightly forked caudal, and a small 

 anal. The vertebral bodies are not solid, but merely constricted 

 cylinders, and the notochord must have been originally continuous 

 through them. The soft parts, of course, are never preserved ; but 

 one specimen of Dercetis from the Lebanon, now in the British 

 Museum (No. 49540), seems to prove that some of these fishes at 

 least were provided with a distensible stomach — a feature so common 

 among existing deep-sea fishes, but not hitherto demonstrated among 

 extinct forms. The fish in question is preserved on a slab of lime- 

 stone, and is shown of two-thirds the natural size in the accompanying 

 photograph (Plate X). In the region which must have been occu- 

 pied by the stomach, it exhibits a comparatively large and deep- 

 bodied fish, with the head pointing backwards towards the tail of 

 the Dercetis ; and the dermal scutes of the latter are displaced in 

 such a manner that there can be no doubt as to the deep-bodied 

 fish having been swallowed head foremost. Judging from other 

 specimens, the normal depth of this Dercetis at the back of the head 

 would be only 10 millimetres, and below the dorsal fin only 13 

 millimetres ; so that the swallowing of a fish 2 2 millimetres in 

 depth necessitates considerable capability of distention. 



Besides being related to the Scopeloids, the Dercetidae of the 



