SOUTH AMERICAN NEMATOGXATHI. 29 



der, the alimentary tract and opercle serve to separate 

 this family from the other Nematognathi. 



Subfamily TACHISUKIN.E. 



ANALYSIS OF THE AMERICAN GENERA AND SUBGENERA OF TACHISURIN^. 



a. Mental barbels none. Head greatly depressed, keeled behind. Occi- 

 pital process becoming narrower behind, meeting the dorsal spine. 



Paradiplomystes VI. 



aa. Mental barbels two. Maxillary barbel broad, baud-like. Pectoral 

 spine and usually the dorsal spine with long band-like filaments. 



AlLURICHTHYS VII. 



ana. Mental barbels four. Maxillary barbels usiifilly short, not band-like. 



Head not greatly depressed. 



b. Palatine teeth in numerous small patches which are aggregated on 

 two fleshy cushions, one on either side of the arched palate. Mandi- 

 bulary teeth disappearing with age. Intermaxillary band of teeth 

 with backward projecting angles of separate patches of teeth. 



GeNIDENS VIII. 



bb. Palatine teeth fixed; both jaws with teeth. Tachisurus ix. 



A. Head and occipital process entirely covered with skin and muscle; 



occiijital process sparingly graniilated. [Galekthyn.) 



AA. Occipital process and bones of the head usually ex^josed, skin 



thin; crown of head' and occipital process granular. 



c. Palatine patches of teeth with a backward projecting angle on 

 the inner margin. 



D. Dorsal plate enlarged. (Sciadeichthi/s.) 



DD. Dorsal plate crescent shaped, not enlarged. 



E. Occipital process narrowed or constricted at base. 



{JVotarius.) 

 EE. Occipital i^rocess widest at base. (Netuma.) 



cc. Palatine patches of teeth without a backward projecting angle 

 on the inner margin. 



F. Eye above the level of the mouth; gill rakers 25 or 

 fewer. 



G. Teeth on the palate villiform. {Ilezanematichthy.s .) 



GG. Teeth on the palate granular; no teeth on vomer. 



Gill membrane not forming a free margin across the 



isthmus. (Tachisurus.) 



FF. Eye not above the level of the mouth; gill rakers long 



and slender, 40 or more. (Cathorops.) 



VI. Paradiplomystes. 

 Paradiplomystes Bleeker, Nederl. Tijdschr. Dierkunde, 

 i, 1863, 92 {coriiscans). 



