14 SIRENOID AND CROSSOPTERYGIAN GANOIDS. 



P. ANNECTENS, OlVen. 



P. ANGUILLIFORMIS, Ow. 



R. amphibia, Peters. 

 P. jEthiopicus, Heckel. 

 L. Arnauldii, Castelnau. 

 L. tobal, Adams. 



Specific Characters. — Those of the genus. 



Formation. — Recent. 



Locality. — Rivers of tropical Africa, Gambia, Senegal, Niger, White Nile, Zambesi. 1 



References. — Owen, Proc. Linn. Soc., p. 29 (1839) ; and Trans. Linn. Soc, vol. xviii, 

 p. 327 (1841); Milne-Edwards, Ann. Sci. Nat. Zool., 2nd ser., vol. xiv, p. 159 (1840); 

 McDonnell, Nat. Hist. Review, vol. vii, p. 94 (I860); Serres, Compt. Rend., Sept. 

 (1863) ; Krauss, Jahresh. d. Vereins fiir Vaterlandische Naturkunde in Wiirttemberg, 

 p. 126 (1864); Klein, ib., p. 134; Dumeril, Hist. Nat. des Poissons, torn, ii, p. 470 

 (1870) ; Gunther, Catalogue, vol. viii, p. 322 (1870). 



A good view of the skull (with description) by Cobbold, Proc. Zool. Soc, 1862, 

 p. 120, pi. xiii. The muscles and cranial nerves are described in Humphry's Observa- 

 tions in Myology, p. 65, pi. v. 



In 1837 a new fish was sent by Dr. Natterer to the Vienna Museum from the river 

 Amazon. It was examined by Eitzinger, who named it Lepidosiren paradoxa, placing 

 it, as we now see, erroneously, in the class of Reptiles, but calling attention at the same 

 time to its piscine affinities. It completely resembled a fish in external form, except that 

 attenuated processes, cylindrical and pointed, occupied the position of the pectoral and 

 ventral fins. It further possessed persistent internal gills, and a spiral valve in the 

 intestine, besides a vertebral column and an organ of hearing comparable only with those 

 of a Fish. But it was found to be furnished with a three- chambered heart, nasal passages 

 communicating with the mouth, 2 and a true paired lung, connected with the 

 oesophagus by an air-duct closed with a glottis, and capable of aerating venous blood. 

 This last hint as to its affinity was regarded for a time as decisive. The presence of a 

 functional lung was then held to be the one test sufficient to separate the class Reptilia 

 (= Reptilia -J- Amphibia of modern naturalists) from the class Pisces. Lepidosiren 



1 The occurrence of the species in different river-basins receives explanation from the physical 

 geography of Africa. " Some of the plains we crossed are flooded to a depth of two or three feet during 

 the rainy season, when the water extends completely across the watershed between the Zambe'si and the 

 Kassabe. * * When flooded, these plains are overspread by numerous fish, consisting principally of a 

 sort of mud-fish and a small minnow-like fry." — Cameron's ' Across Africa,' vol. ii, p. 168 (1877). 



2 Owing to the imperfection of his specimen, these were at first described as blind sacs by Professor 

 Owen in his account of Protopterus. 



