SOUTH AMERICAN NEMATOGNATHI. 9 



b. Dorsal and anal nearly co-extensive with the cau- 

 dal portion of the vertebral column; opercle pres- 

 ent. Chackhv, Plotomla', Clariida.'. (Exotics.) 



bh. Dorsal short, confined to the abdominal portion 

 of the vertebral column. 



c. Opercle none; adipose fin none; neural spines 

 of the coalesced vertebras forming a ridge from 

 the occipital to the dorsal. Gill-opening re- 

 duced to a slit in front of the pectorals. Cau- 

 dal vertebras greatly compressed, their neural 

 spines expanded. Bunocephalidj*: i. 



a. Tail short, veut nearly equidistant from tip of snout aud base of cau- 

 dal. Anal with less than 10 rays Bunocephali7i'i'. 

 cut. Tail long; veut in anterior third of body; anal with 50-60 rays. 



Platystacina;. 



cc. Opercle well developed and movable; adipose 

 fin normally present; occipital process sometimes 

 forming a bony bridge from the occipital to the 

 dorsal plate. Gill openings usually wide. Cau- 

 dal vertebrae not compressed, the neural spines 

 simple, spine-like. 



d. Maxillary well developed, provided with teeth 

 and forming the sides of the jaw; nares approx- 

 imated; gill membranes somewhat joined, but 

 free from the isthmus. Diplomystid.e ii. 



dd. Maxillary vestigiary, the intermaxillaries 

 only forming margin of upper jaw. 



SlLURID^ III. 

 «. Gill membranes usually entirely free, sometimes united and forming 

 a free membrane across the isthmus, or in some species of Tachisurus 

 joined to the isthmus. 



b. Anal much shorter than the cai;dal portion of the vertebral column; 

 nares withoi;t barbels. 



c. Nares approximated (partly marine). TachlsurhiK. 



cc. Nares remote; barbels six; adiiDose fin well developed. 



d. Teeth incisor-like, in two series in the upper, in a single series 

 in the lower jaw. Callophy since. 



