112 



LOWER VERTEBRATES. 



All the Neraatognatlii are carnivorous fishes. Most of them inhabit fresh waters, 

 but many are found in the sea. The latter, however, never venture to any consider- 

 able depths, and most of them sometimes ascend the rivers. None are deep-sea 

 fishes. They are most abundant in tropical waters, a greater variety of species being 

 found in South America than in any other continent, although the rivers of Africa 

 also teem with them. Few of them reach the colder parts of the temperate zones. But 

 one species {Silurus glanis) is found in Europe, and none, either marine or fluviatile, 

 inhabit the waters of the United States west of the Rocky Mountains, their range in 

 the eastern Pacific not extending north of the Gulf of California. 



In size the Nematognathi vary greatly : from two inches in length to six feet or 

 more. Few of them are much valued as food ; most of them, especially the marine 



species, having rather tough and flavorless 

 flesh. 



As to the origin of the Nematognathi, the 

 following remarks of Professor Cope seem to 

 me reasonable: "This division is the nearest 

 ally to the sturgeons (Chondrostei) among 

 Physostomous fishes, and I imagine that 

 future discoveries will prove that it has been 

 derived from that division by descent. . . . 

 The aflinity of the cat-fishes to the sturgeons 

 is seen in the absence of symplectic, the rudi- 

 mental maxillary bone, and, as observed by 

 Parker, in the interclavicles. There is a sujjer- 

 ficial resemblance in the dermal bones. The 

 rudimental mesopterygium shown by Gegen- 

 baur to exist in the young SiluridiB, the pras- 

 coracoid arch, and the ventral fins, are shared 

 with the sturgeons and other divisions." 



One of the families (Hypophthalmidae) 

 at present referred to this order, differs from 

 all others, according to Cope, in having the 

 lower pharyngeals united for tlieir whole 

 length. 



The Nematognathi are all placed by Dr. 

 Giinther in a single family, Siluridffi. This 

 is certainly unnatural, as the differences between many of the different members 

 of the group far outweigh the distinctions existing between the currently recognized 

 families of Acanthopteri. Professor Cope divides them into three families, Silurids3, 

 Aspredinidse, and Hypophthalmidas. Professor Gill arranges them in eleven families. 

 The present writer has had no opportunity to form a definite opinion of the value of 

 most of these families, but for the present is disposed to follow Professor Gill's 

 arrangement. The different families now follow in order. 



The family of Aspeedinid^ is characterized especially, according to Coj)e, by the 

 absence pf the opercle. The adipose fin is wanting, and there is no spine in the dorsal. 

 Tlie eyes and mouth are small. There are six barbels. The gill opening is reduced 

 to a small foramen. The skin is either smooth or covered with bony lumps or 

 tubercles. About ten species are known, all from the fresh waters of the north- 



FiG. 76. — Abdomen of Platysiacus batraclms, with 

 the ova attached : at a some have been removed. 



