574 Mr. C. T. Regan on the 



formed by the parapophyses of tlie fourth and fifth vertehi'fe 

 and by the upper limb of the supra-cleitlirum. The vertebrte 

 number 66 (14 + 512), the first five aukylosed ; the ribs are 

 inserted on parapophyses. 



Family 20. Trichomycteridae. (Fig. 2, B.) 

 Body naked, moderately elongate. Gill-openings wide or 

 restricted. Dorsal fin short, without spine ; no adipose fin ; 

 anal short or moderately long ; pelvics 5- or 6-rayed. 

 Nostrils remote, the anterior sometimes with a barbel : 

 teeth in jaws villiform or incisor-like; palate sometimes 

 toothed. Palatine broad ; pterygoid absent ; mesopterygoid, 

 when present, very small, attached to inner edge of meta- 

 pterygoid, Avhich joins palatine. Skull depressed, contracted 

 between and expanded behind the orbits. Post-temporal 

 absent ; upper limb of supra-cleithrum suturally united to 

 supraoccipital and pterotic; mesocoracoid present; hypo- 

 coracoids narrowed forward below, pointed anteriorly, not 

 interlocking. Vertebrae 42 to 46 (19-21 + 23-;25) ; ribs on 

 parapophyses ; fifth vertebra ankylo^ed with the complex, 

 w hich is short, rigidly attached or ankylosed to the skull, 

 and bears a pair of transverse subcylindrical capsules with 

 lateral openings; air-bladder divided into two lateral sacs 

 enclosed in the bony capsules. 



Fresh watir fishes of South America. 



The principal genera may be arranged thus ; — 



I. Air-bladder capsule formed by tbe parapophvsis of the fourth 



vertebra, in front free from the skull and noruDally attached to 

 the supra-cleithrum, behiud free from the normal jfliapoj.hysis of 

 the fifth vertebra; dor.«nl tin anterior; opercles unarmed; one 

 pair of maxillary barbels. (Cetopsitiee.) 



Ct-iopsis. 



II. Air-bladder capsule united to the skull, its anterior wall includinf^ 



the lower limb of supra-cleithrum and a part of the exoccipital 

 and epiotic bones ; paiapophysis of fifth vertebra not developed 

 as a sejarate process; dorsal tin median or posterior. {Tricho- 

 im/cteihue.) 



A. Opercles unarmed ; one pair of maxillary barbels. 



Ntmatocjetiys, 



B. Operculum and intoroperculum armed with spines. 

 One pair of maxillary barbels Stciiophil>t,<, Tmidellia. 



Two pairs of maxillary barbels '/'ric/ioun/crerus, Eiemophilux, 



TiithiK, I\irii>(i(iHf Minioij/nnis. 



Family 21. Bunocephalidae. 

 Gill-openings reduced to a small foramen in front of tlie 

 pectoral fin. Dorsal fin anterior; no adipose fin; caudal 



