FISHES. 173 



that it occurs again in a very singular fisli, Aphredoderus sayanus, which inhabits 

 the same geographical range. 



As to the habits of the blind-fish, I quote as follows from Professor Cope. 



" If these Amhh/opscs be not alarmed, they come to the surface to feed, and swim 

 in full sight like white aquatic ghosts. They are then easily taken by the hand or net 

 if perfect silence be preserved, for they are unconscious of the presence of an enemy, 

 exce])t through the sense of hearing. This sense is, however, evidently very acute, 

 for, at any noise, they turn suddenly downward and hide beneath stones, etc., at the 

 bottom. Tiiey must take much of their food near the surface, as the life of the dei)ths 

 is apparently very sparse. This habit is rendered easy by the structure of the fish, for 

 the mouth is directed upwards, and the head is very flat above, thus allowing the 

 mouth to be at the surface." 



Sub-Order V.— XENOMI. 

 This sub-order contains but a single family, the Dalliid^e. In all external respects 

 the Xenomi resemble the Haplomi, but the structure of the pectoral elements of the 

 skeleton distinguishes them sharply from all other soft-rayed fishes. 



But one species of Dalliidaj is yet known. The black-fish of Alaska and Siberia 

 {Dallia pectorcdis) reaches a larger size than the mud-minnow, and is more pike-like in 

 appearance. It furnishes a very important article of food to the natives of these 

 northern regions, in which it is the only fresh-water fish, except the Salnionida3. 



D. S. Jordan. 



Sub-Order VI. — SYNENTOGNATHI. 

 Intermediate between the typical Physostomous and Physoclistous fishes are certain 

 forms which have been segregated into a sub-order under the name Synentognathi. 

 The air-bladder is destitute of a communication with the intestinal canal, and the 



Fig. 108. — Scomberesox saurns, skipper, bill-flsli. 



fishes are to that extent physoclistous; but there are no spines to the dorsal, anal, oi 

 ventral fins, and consequently these forms more nearly resemble the great majority of 

 physostomous fishes; the ventrals are also, as in the latter, abdominal in position. On 

 the one hand the species in question are closely related to the Haplomi, and on the 

 other to the Percesoces ; and this resemblance, which is manifested in many structural 

 characteristics, is extended by the likeness in external a])]iearance. Two families have 

 been distinguished among the representatives of this sub-order, the Exocastidie and 

 the Belonidae. 



The flying-fishes are the representatives of a family somewhat numerous in species, 

 comprising, in addition to the flying-fishes themselves, several types of special interest, 

 whose extremes differ considerably from the flying-fishes, but which are, nevertheless, 

 connected together by such gradations as to retuler it evident that the family is quite 

 a natural one. The name Exoccetid.e should by rights be used for the fninily. 

 Several well-marked groups or sub-families are embraced in it. 



