Classification of the Order Ostariophysi. 557 



specialized Bagrids, A.rablycepidae, Sisoridse, Amphiliidae, 

 Chdcidae, Schilbeidse^ Clariidse, Paugasiidse, Synodontidse, 

 and Malopteruridae. The neotropical Siluroids (except the 

 Doradidae) come last, and these begin with the Pimelodidse, 

 which represent the Bagridse in South America, and are 

 followed by the Helogeuidse, Hypophthalmidse, Tricho- 

 mycteridse, and Bunocephalidse, ending with the highly 

 specialized Callichthyidse and Loricariidae, which are the 

 most aberrant fishes of the order. 



Family 1. Diplomystidae. (Fig. 2, C.) 



Body naked, moderately elongate. Gill - membranes 

 united, but free from isthmus. Dorsal fin anterior, with a 

 spine ; adipose fin present ; anal short ; pclvics 6-rayed ; 

 pectoral with a spine. Nostrils close together ; a pair of 

 maxillary but no other barbels ; prsemaxillaries fixed ; max- 

 illary well developed, toothed, expanded distally, and proxi- 

 mally articulated with both heads of the palatine ; bands of 

 villiform teeth in jaws, obtuse teeth on the vomer. Palatine 

 forked anteriorly; no pterygoid; meso pterygoid very small, 

 connecting metapterygoid with vomer; metapterygoid at- 

 tached to palatine anteriorly and to orbitosphenoid internally; 

 head of hyomandibular broad, articulating with pterotic, 

 sphenotic, and alispheuoid. Post-temporal present; supra- 

 cleithrum forked ; mesocoracoid present ; hypocoracoids 

 narrowed forward below, not meeting. Vertebrae 42 (17 + 25) ; 

 ribs on parapophyses ; fifth vertebra rigidly attached to 

 complex, but not forming interlocking sutures ; para- 

 pophysis of fifth vertebra normal, of fourth a transverse 

 lamina with a stout somewhat decurved anterior process 

 firmly attached to the stem of supra-cleithrum ; first centrum 

 well developed, separating complex from basioccipital. 



Diplomystes papillosus from Chili and Argentina. 



In all the remaining Siluroids the maxillary is slender, 

 toothless, and the fifth and complex vertebrae unite by inter- 

 locking sutures or are ankylosed or united by investing bone. 



Family 2. AriidaB. 



Naked, moderately elongate ; gill-membranes united, 

 forming a fold across isthmus. Dorsal fin anterior, with a 

 spine ; adipose fin present ; anal short or of moderate 

 length; pelvics 6-rayed; pectoral with a spine. Mouth 

 terminal ; teeth in jaws and often on palate ; nostrils 

 usually close together, without barbel ; maxillary and one or 

 two pairs of mandibulary barbels. Epiotics with posterior 



