CAVE-FISH. 437 



fins to a narrow-rayed fringe, with the first ray elongated, more or less completely 

 received in a longitudinal groove. There is a band of teeth in the jaws, and another 

 on the vorner, and all the species have barbels, not only on the chin, but likewise 

 on the muzzle, the number of these appendages affording the readiest means of 

 specific discrimination. They are all of small size, and while ranging over the 

 same seas as the ling, likewise extend to those of Japan, the Cape, and New 

 Zealand. The British representatives of the genus include the five -bearded 

 rockling (M. mustela), with four upper barbels, the four-bearded rockling (M. 

 cimbria), and the common three-bearded rockling (M. tricirrhata) ; the little fish 

 commonly known as the mackerel-midge, and formerly regarded as the representa- 

 tive of a distinct genus being only the young of the rocklings. 



Brief mention may be made here of a fish from the Northern, Temperate, and 

 Arctic seas, known as the torsk (Brosmius brosme), on account of its forming the 

 sole representative of a group characterised by having only a single long dorsal 

 and a shorter single anal fin, the caudal being distinct, the narrow pectorals formed 

 of five rays, teeth present on the vomer and palatines, as well as in the jaws, and 

 the chin furnished with a barbel. Attaining a length of a little over 20 inches 

 the torsk is occasionally taken in the Firth of Forth, and is abundant round the 

 Shetlands and Orkneys. 



SAND-EELS AND THEIR ALLIES, Family OPHIDIID^. 



In this rather small family, almost all the members of which are marine, the 

 pelvic fins, if developed at all, are rudimentary ; there is no separate anterior dorsal 

 or anterior anal, and the caudal is generally confluent with the median fins. In 

 form the body is more or less elongate, but it may be either naked or scaled. 

 The dorsal fin occupies the greater portion of the back ; the rudimentary pelvics 

 are jugular in position ; the gill-openings are wide ; and the gill-membranes are not 

 attached to the isthmus. While some of these fishes are deep-sea forms, others are 

 littoral. The family may be divided into five subfamily groups. 



The most remarkable representatives of the first subfamily (in 

 which pelvic fins, attached to the pectoral girdle, are always present) 

 are two small fishes from the subterranean fresh waters of certain caves in Cuba, 

 constituting the genus Lucifuga. They are totally blind, with the eyes rudi- 

 mental and covered with skin, or wanting, and always live in perpetual darkness. 

 The cave-fish are closely allied to certain small fishes from the Tropical Atlantic 

 and Indian Oceans forming the genus Brotula, and characterised by the elongate 

 body being covered with minute scales, the moderate-sized eyes, the reduction of 

 each pelvic fin to a single filament, of which the extremity may be split, the 

 villiforrn teeth, and the presence of barbels on the muzzle ; these barbels being 

 reduced in the cave-fish to small tubercles. With the exception of these cave- 

 fish, all the members of this family are marine forms ; and it is very curious that 

 among the latter there are two very rare species, respectively constituting the 

 genera Typhlonus and Aphyonus, found at great depths in the southern oceans, 

 which are also completely blind, and apparently unprovided with any phosphorescent 

 organs. 



