110 LOWER VERTEBRATES. 



The Saccophaeyngid^ have been long but very imperfectly known. The typical 

 form was first described by an American naturalist, Dr. S. L. Mitcliill, of jSTew York, 

 in 1824. The only specimens that have been thus far obtained liave been found at the 

 surface, gorged with fishes larger than themselves. They thus contrast, as to their 

 habits, witli the Eurypharyngida^, and their structure would at once indicate a differ- 

 ence of habits. They have, like their kindred, a small head and elongated jaws, but 

 the elongation is quite moderate compared with those of the Eurypharyngids. They 

 have also large raptorial teeth in one or both jaws, well fitted for seizing and holding 

 prey. 



Both of the types of lyomerous fishes have very peculiar pedunculated appendages 

 in the place of the lateral line. Their entire organization, in fact, is peculiar to the 

 extent of anomaly, and our old conceptions of the characteristics of the fish class re- 

 quire to be modified in the light of our knowledge of such strange beings. 



Oeder IV. — OPISTHOMI. 



For want of a better place, we have next to consider another singular gi'oup of 

 fishes, whose members have been widely separated in the s}-stem. For example, Dr. 

 Giinther associated one family (the Mastacembelidse) with the Blennies in the ' tenth 

 division' of the ' Acanthopterygii,' and isolated another (the Notacanthidse) in a 

 peculiar group, the ' nineteenth division ' of the ' Acanthopterygii.' Professor Cope 

 distinguished the Notacanthids as a peculiar order (Opisthomi) of physoclistous fishes, 

 and ignored the Mastacembelids. The two families, however, appear to be related, 

 and may both be referred to tlie same order. 



The Opisthomes are teleosts with the jaws complete and differentiated, the scapu- 

 lar arch not connected with the cranium but suspended to the vertebral column, the 

 back armed with numerous spines, and with ventrals abdominal or suppressed. 



The Mastacembelids have an elongate, eel-like body, a produced lower jaw, the 

 dorsal very long and mostly composed of sliort free spines, but with a small rayed por- 

 tion behind, the anal elongated and with about three spines in front, and without 

 ventral fins. The species are inhabitants of the fresh waters of the East Indies and 

 neighboring parts of Asia. 



The NoTACAXTHiBs are also elongate fishes, the spines of the back are short and 

 free, and behind them is one soft ray, or perhaps none ; the anal is very long, and 

 chiefly composed of rays, and abdominal venti-als exist which have each several inar- 

 ticulate and more than five branched rays. The species are marine, and live generally 

 in cold water of considerable or even great depths. 



Theodoee Gill. 



Order V. — NEMATOGNATHI. 



The fishes of this order agree in having the maxillary bone imperfectly developed 

 and forming the basis of a long fleshy feeler or barbel. This cliaracter has suggested 

 the name Nematognathi, given to the order by Dr. Gill. The analogy of these bar- 

 bels to the whiskers of a cat has given rise to the vernacular name of cat-fish, by 

 which the members of the order are known in the United States. Other external 

 characters of importance, distinguishing them from the great body of teleostean 

 fishes, are the absence of the subopercle, and the absence of true scales, the skin being 



