74 CLASS XIV. 



distinguishes various other species. They are fresh-water fishes of the uew 

 world, principally from N. America. 



The caudal fin, as in the sturgeons and sharks, is attached to the under 

 side of the vertebral column. The spinous covering of the first fin-rays 

 (Agassiz names these parts fulcra) is a character which also occurs in 

 many Ganolepidoti of the former world. There is a half gill attached to 

 the gill-cover. A swimming-bladder is found, entirely cellular and very long, 

 extending to the anus; it is divided into two lateral halves, and communi- 

 cates by a longitudinal opening {glottis) with the oesophagus below the up- 

 permost ossa phary7igealia ; see my figure of it in Mueller's Archiv, 1841, 

 Tab. S. Fig. 4. The anatomy of this fish has been illustrated principally by 

 the investigations of JoH. Mueller in his work lately cited, Uber den Bau 

 und die Grenze der Ganoiden. 



Polypterus Geoffr. Head oval, rotvmdate anteriorly, depressed 

 above. Two cirri above the mouth. Two spiracles at the sides of 

 head. Scales hard, osseous, rhombic, arranged in rows running 

 obliquely backwards. Branchiostegous membrane with a single, 

 flat ray. Caudal fin rotundate. Dorsal fins numerous, all sup- 

 ported anteriorly by a single ray sustaining soft transverse rays at 

 its posterior margin. Anal fin small, situated near the caudal. 



Sp. Polypterus bicJdr Geoffrot Saint-Hilaire, Ann. du Mus. i.1802, pp. 

 57 — 68, PI. v., Agassiz Poiss. foss. 11. Tab. c ; with 16 dorsal fins ; this 

 fish lives in the Nile, and attains a size of about 2' ; another species from 

 the Senegal has only 10 dorsal fins, Pol. Senegalus CuviER, Guerin Magas. 

 de Zool. 1839, Poiss. PI. I ; finally, a third species from the WJiite Nile has 

 lately become known under the name of Polypterus Eadlicheri, in KoTSCHY 

 Ahhildungen u. Beschreihungen neucr Thiere u. PJlanzen. Stuttgart, 1849, 

 Tab. XXII. fig. I ; it has 12 dorsal fins. 



These fishes have no gill on the gill-cover. The swimming-bladder is 

 long, sacciform, double, and without cells, with fine longitudinal folds in- 

 ternally. It opens on the under side of the oesophagus. See Geoffrot op. 

 cit. p. 65, and J. Mueller in his Archiv, 1841, s. 224, 225. F. Leydig 

 Ilistologische Bemerhungen iiher Polypterus hichir. Zeitschr. fur wissenscJi. 

 Zool. V. s. 40 — 74, Taf. II. III. 



Arnia L. Head osseous, depressed, rotundate anteriorly. Nasal 

 cirri two. Body covered with large scales, rounded at the free mar- 

 gin. Branchiostegous membrane with 10 — 12 rays. Dorsal fin 

 long, depressed. Anal fin short. Caudal fin rotundate, with rays 

 adhering to the inferior and posterior margin of vertebrse running 

 obliquely upwards through the fin. 



There are various species of this genus, all from fresh-water in North 

 America. What species LiNN^US indicated by his Amia calm cannot 

 be determined with certainty ; see Valenciennes in Cuvier et Valen- 

 ciennes Hist. nat. des Poissons, xix. (1846), pp. 402 — 432.-^.4»Ma calva 



