GANOIDEI. 355 



SECOND SUB-OEDER— ACANTHODINI. 



Extinct. Body oolong, compressed, covered luith shagreen ; 

 skull not ossified ; caudal heteroccrcal. Large spines, similar 

 to those of Chondropterygians, in front of some of the median 

 and paired fins. The spines are imbedded hetiveen the muscles, 

 and not provided with a proximal joint. 



Acanthodcs, Ohiracanthus, from Devonian and Carbonifer- 

 ous formations, 



THIRD SUB-ORDER— DIPNOI. 



Nostrils two pairs, more or less within the mouth ; limbs 

 with an axial skeleton. Lungs and gills, Skeleton nolo- 

 chordal. JSfo branchiostegals} 



EiKST Family — Sirenidj-;, 



Caudal fin diphycercal ; no gular plates ; scales cycloid. A 

 pair of molars, above and below, and one pair of vomerine teeth. 



Lepidosiren. — Body eel-sliaped, with one continuous vertical 

 fin. Limbs reduced to cybndrical filaments, without fringe. 

 Vomerine teeth conical, pointed. Each dental lamina or molar 

 with strong cusps, supported by vertical ridges. No external 

 branchial appendages ; five branchial arches, with four interven- 

 ing clefts. Conus arteriosus with two longitudinal valves. 

 Ovaries closed sacs. 



One species only is known from the system of the River 

 Amazons {L. 'paradoxa). It must be very locally distributed, 

 as but a few specimens have been brought to Europe, and all 

 recent endeavours to obtain others have been unsuccessful. 

 Natterer, by whom this most interesting fish was discovered, 

 states that he obtained two specimens, one on the Madeira 

 River, near Borba ; the other in a backwater of the Amazons, 

 above Villa Nova. The natives of the former place called it 

 Caramurii, and considered it very scarce. The larger indivi- 



1 See pp. 73 and 74, Figs. 35 and 36. 



