150 



cleft of the mouth exceedingly wide. A long elastic muscular band passing from 

 the hyoid bone to the inner aspect of the mandibular symphysis. Teeth acute, 

 unequal, in single series in premaxilla?, maxilla?, mandibles, and palatines ; none 

 on the tongue. Bye moderate. Gill-covers rudimentary. One dorsal fin 

 opposite to the anal, situated in the posterior fourth of the body, near the caudal. 

 No adipose dorsal. No pectoral fins. Ventral fins situated in the anterior half 

 of the body. Gill-openings very wide. No air-bladder. 



A large luminous organ behind the orbit : two long rows of small luminous 

 organs on either side of the body, on the ventral aspect, from the gill-opening to 

 or nearly to the caudal fin. 



Distribution : North Atlantic and Azores ; both sides of the Bay of Bengal. 



122. Pliotostomias atrox (Alcock). 



Thaumastomias atroz, Alcock, Ann. Mag. Nat. Hist., Sept. 1890, p. 220, pi. viii fig. 7, and Aug. 1898, p. 147: 

 Illustrations of the Zoology of the Investigator, Fishes, pl. XXX. fig. 2. [See also Goode and Bean, Oceanic 

 Ichthyology, fig. 141, which, however, has been incorrectly copied from my figure in the Annals and Magazine of 

 Natural History, a second large post-orbital luminous organ, of which there is no trace either in the specimen or 

 in my drawing and description, having been added. 



D. 23. A. 25. C. eirc. 25. P. 0. V. 6. 



Length of the head one-fifth, height of the body one-tenth, of the total 

 without the caudal. 



Snout truncated, broad, with a slightly concave vertical profile, its length 

 one-third the diameter of the eye. Eye large, circular, its diameter about one- 

 fourth the length of the head ; interorbital space wider than the eye, convex. 

 On each side there are two luminous organs, one about the size and shape of a 

 caraway-seed, below and partly in front of the eye, the other large, salient, 

 slipper-shaped, and more than one-third the length of the head, lying parallel 

 with the upper jaw behind the eye. Mouth enormous, its cleft as long as the 

 head ; its floor is completely wanting except quite anteriorly, its place being 

 taken by a long elastic muscular band which extends from the tip of the hyoid to 

 the inner surface of the mandibular symphysis ; the mouth-cleft and the gill-cleft 

 being thus continuous beneath, almost divide the head from the rest of the body ; 

 the lower jaw projects beyond the upper. Teeth, everywhere except in the 

 maxilla, in the form of slender acute rigid fangs ; in each premaxilla eight or 

 nine, and three remote stouter ones at the symphysis; in each half of the 

 mandible an uneven row of over twenty, and five (one median flanked on each 

 side by a pair) of superior size at the symphysis ; in each palatine a row of seven 

 or eight, increasing in size from before backwards, and a patch on the upper 

 pharyngeal bones; maxillary teeth in the form of even, close-set, recurved 

 serrations, of which there are over thirty in each bone. 



