BONY FISHES AND GANOIDS. 485 



extraordinary development of fin-rays observed in the whole class of fishes, 

 some of them being several times longer than the body, and provided with 

 lappet-like dilatations. There is no doubt that fishes with such delicate ap- 

 pendages are bred and live in depths where the water is absolutely quiet, as a 

 sojourn in the disturbed water of the surface would deprive them at once of 

 organs which must be of some utility for their own preservation." Riband- 

 fishes are classed under three genera, respectively known by the names of 

 Begalecus, Stylophorus, and Trachypterus. Of these, the first includes the 

 largest known species ; Banks' riband-fish (R. banksi), which is occasionally 

 cast 011 the shores of England, where it is known most inappropriately as 

 the " king of the herrings," exceeding a score of feet in length. In place of 

 the horn of the unicorn-fish, this riband-fish has a crest of curving spines on 

 the crown of the head, which recalls the feathery crest of a cockatoo. In 

 this genus the pelvic fins, which are placed almost immediately behind the 

 extremely short pectoral pair, are reduced to long tapering filaments, withr . 

 out rays ; the caudal fin being rudimental or absent. On the other hand, in 

 the rare Stylophorus, the pelvic fins are totally absent, and the caudal forms 

 a very long appendage like a whip-lash. In the typical Trachypterus, how- 

 ever, the pelvic pair of fins still retain their rays. The best known member 

 of this genus is the northern one commonly known as the deal-fish, which is 

 not unfrequently cast ashore after gales on the mainland and islands of the 

 north of Britain. 



An aberrant group of the sub-order is formed by the long-bodied deep-sea 

 fishes, commonly known as thorn-backs, all of which may be included in the 

 single genus Notacanthus. In these fishes the dorsal fin 

 has no soft portion, and is composed of a great number of Section Nota- 

 low tooth-like spines, separated from one another by com- canthiformes. 

 paratively long intervals, and extending over nearly the whole Family Nota- 

 length of the back, the long anal being of somewhat similar canthidce. 

 structure. The muzzle is produced some distance in advance 

 of the snout. The pectoral and pelvic fins are widely separated from one 

 another, so that the latter are truly abdominal in position ; but in sp}te of 

 this the caudal region extends a long distance behind the pelvics, the tail 

 terminating in a sharp point, without a distinct fin. 



The members of the last sectional group of the great sub-order Acantho- 

 pterygii are distinguished from nearly all the forms hitherto mentioned by the 

 coalescence in the median line of the lower pharyngeal bones. 

 On this account the group has been regarded as of subordinal Section Pharyn- 

 value, although it seems preferable that it should rank only gognathi. 

 as a section. That it is a specialised group is indicated, not Family 



only by the union of the pharyngeals, but also by the loss of Pomacentridce. 

 the air-bladder. The group includes four families, of which 

 the first is represented by the coral-fishes, forming the genera Dascyllus, Heli- 

 astes, Pomacentrus, etc. Most of these are inhabitants of the tropical seas, 

 where, as their name implies, they frequent coral reefs. In form and colora- 

 tion, as well as in habits, they are very similar to the Chcetodontidce (p. 465), 

 many of them having alternate dark and light bands on the body. The 

 absence of scales on the fins in the present family serves, however, to dis- 

 tinguish them at a glance from the members of the other group. In these 

 fishes the body is deep and compressed ; the scales are of the ctenoid or 

 comb-like type ; the lateral line is either interrupted, or stops short of the 

 caudal fin ; and false gills are developed in the head. The number of species 



