LEPIDOSIREN— PROTOPTERUS. 13 



two, pointed, imbedded in the mesethmoid cartilage. Pectoral fin without fringe. Ventral 

 Jin without fringe. Vertical fin continuous. Scales cycloid, with a minute reticulate 

 pattern, covering all the body except the fore- and part of the hind-limb. Lateral line 

 central, extending from head to tail. Branchial arches five; no gills upon first, second, 1 

 or fifth in adult ; no spiracle ; no pseudobranchia ; opercular gill rudimentary ; no 

 external gills as yet known. Air-bladder double, lung-like. Heart with two incom- 

 pletely separated auricles ; incomplete ventricular septum. Optic nerves not decussating. 

 Intestine straight, with spiral valve ; no distinction of large and small intestine ; rectum 

 communicating with urogenital sinus. Oviducts with dilated peritoneal opening; not 

 united with ureters ; entering urogenital sinus by a common opening. Abdominal pore 

 single, in front of vent. 



L. paradoxa, Fltz. 



Specific Characters. — Those of the genus. 



Formation. — Recent. 



Locality. — River Amazon and tributaries. 



References. — Fitzinger, Isis, p. 379 (1837); Natterer, Ann. Wien. Mus., ii, p. 165, 

 (1839) ; BischofT, Lepidosiren paradoxa, anatomisch untersucht und beschrieben, Leipsic, 

 (1840), translated in Ann. Sci. Nat., vol. xiv, p. 116 (1840) ; Hyrtl, Abh. Bohm. Gesell., 

 vol. iii, p. 605 (1845) ; Heckel, Mull. Arch. Nat., p. 534 (1845); Dumeril, Hist. Nat. 

 des Poissons, torn, ii, p. 467 (1870); Gunther, Catalogue, vol. viii, p. 322 (1870). 



Genus Protopterus, Owen. 



Rhinocryptis, Peters (Lepidosiren of many authors). 



Pectoral and ventral fins fringed on the post-axial border by a cutaneous fold sup- 

 ported by rays, several of which spring from each joint of the axis. Three rudimentary 

 external gills persist to the adult state. Branchial arches six; the first and sixth with a 

 single gill, none on the second and third. About thirty-six pairs of ribs. In most 

 other respects similar to Lepidosiren. 



1 Hyrtl found a gill on the posterior edge of the second arch in his example. 



