SOUTH AMERICAN NEMATOGNATHI. . 221 



Doras Cuv. & Val., Hist. Nat. Poiss. xv, 267, 1840 

 {costatiis). 



CentrocJdr Agassiz; Gen. et Spec. Pise. Bras. 14, 1829 

 (crocodili) . 



Lithodoras Bleeker, Nederl. Tijdschr. Dierkunde, i, 

 84, 1863 (lithogaster). 



Pterodovas id. 1. c. {granulosus). 



Platydoras id. 1. c. 86 (costatus). 



Acanthodoras id. 1. c. {cataphractus) . 



Astrodoras id. 1. c. (aster if rons). 



Amblydoras id. 1. c. {ajjinis). 



Zathorax Cope, Proc. Phil. Acad. Nat. Sci. 1872, 271 

 {r)ionitor)= Astrodoras Bleeker. 



Agamyxis Cope, Proc. Amer. Philos. Soc. xvii, 101, 

 1878 (pedinif^'ons) . 



Type: Silurus costatus Linnaeus. 



The numerous genera into which this group has been 

 divided seem to us hardly tenable. It is true that if 

 only the types of these genera existed they might be 

 separated generically, but if the other species are taken 

 into consideration the intergradations are too perfect to 

 admit of division. 



Prof. Cope (Proc. Acad. Nat. Sci. Philad. 1874, 133) 

 says: "Doras heckelii pertains to this genus " (i. e. Zatho- 

 rax), D. hekelii is certainly congeneric with D. asteri- 

 frons, the type of Astrodoras of which Zathorax is there- 

 fore a synonym. 



Anterior nares on or near the upper lip; snout short, 

 the eye in anterior half of the head; teeth well devel- 

 oped; adipose fin usually with a well defined anterior 

 margin. 



Habitat: Rio Plata; Rio San Francisco and the rivers 

 north of it. No species of Doras have as yet been found 

 in the Parahyba, Rio Doce and Jequitinhonha. Two 

 species are found in the San Francisco. 



