206 THE VOYAGE OF H.M.S. CHALLENGER. 



Echiostoma, Lowe.^ 



Echiostoma barbatum (PI. LIII. fig. B). 



Echiostoma barbatum, Lowe. Proc. Zool. Soc. Lond., 1843, p. 88. 

 „ „ Giinth., Fish., vol. v. p. 427. 



„ „ Goode and Bean, BulL Essex Instit., vol. xi. p. 128. 



B. 12. D. 12-15. A. 16-18. P. 3-5. V. 8. 



The head and body of this fish are compressed, scaleless ; its greatest depth is one- 

 eighth of the total length, the length of the head nearly one-seventh. The upper part of 

 the head is short, the cleft of the mouth very wide, extending to the angle of the 

 prseoperculum, the hind margin of which consequently descends backwards in a strongly 

 oblique direction. The opercular portion is very narrow, and the whole gill-cover formed 

 by thin, almost membranous plates. The width of the interorbital space much exceeds 

 that of the orbit, the diameter of which is one-sixth of the length of the head, and a 

 little less than that of the snout. Lower jaw but slightly projecting beyond the upper. 

 Nostrils, two round openings on each side, situated in a cavity on the upper side of the 

 snout, and separated from the orbit by a slight crenulated projection ; also the median 

 ridges on the upper side of the head are indistinctly crenulated. 



The formidable dentition consists of pointed teeth unequal in size, chiefly arranged 

 uniserially, all the larger ones being depressible backwards or inwards. The two large 

 front teeth of the upper jaw leave a wide space for the reception of the lower teeth. 

 When complete, the intermaxillary dentition consists of ten teeth, of which the first is 

 the smallest and readily lost, the third and sixth the largest. The maxillary dentition is 

 peculiar, inasmuch as its proximal third consists of six teeth of moderate size, while the 

 two distal thirds are formed by uniformly small teeth, there being no gradual transition 

 from the larger to the smaller teeth. The mandibulary teeth are uniserial in front, 

 biserial behind; the seven anterior teeth are larger than the rest, and the third and 

 sixth exceed the others. Vomer with a fang on each side ; palatine with a series of 

 small teeth. Two pairs of fangs, strongly curved backwards, on the tongue. Also the 

 upper pharyngeals bear some teeth of rather small size. 



The gill-laminae are well developed, except on the hinder part of the horizontal 



1 This genus seems to have been re-named Hyperchoristus (Gill, Proc. U.S. Nat. Mus., vol. vi. 1884, p. 256); its 

 dentition is described thus : — " Teeth on the jaws nearly uniserial, but in several groups, of which the successive teeth 

 (about four) rapidly increase in size backwards, and teeth on the palate enlarged, one on each side of the vomer, and 

 several on the palatines." A single specimen, named Hyperchoristus tanneri, of which the size is not stated, was 

 obtained by the U.S. Fish Commission in the North Atlantic (lat. 40° 26' N., long 66° 58' W.), at a depth of 

 956 fathoms; but as the specimen is said to have been "so lively when brought to the surface that it twisted itself 

 round in its attempt to bite the commander of the vessel," it is more likely to have been captured much nearer to the 

 surface of the water. 



