102 



Sauroids.- 



-FISHES.- 



-POLYPTEKIDS. 



irig parts of Canada, wherein about ten species have 

 been detected by Agassiz, and they are considered to 

 be the nearest representatives now Hving of the extinct 

 ganoid fishes. 



In this family the upper jaw, which is elongated in 

 the axis of the fish, is composed of several pieces ; and 

 the mandible is also composed of many pieces, as in 

 the reptiles. The vomer is of two pieces, separated 

 by a median cleft. Instead of the first vertebra 

 being united to the occipital bone by opposuig cups 

 filled with an elastic gelatinous fluid as in ordinary 

 fishes, that joint is formed by a ball and socket, so that 

 the head laas a nodding movement. Tlie olfactory 

 organ, situated at the tip of the upper jaw, contains 

 the ordinary nasal folds arranged simply. The gills, 

 on four arches, have a perfect bifoliate stnicture, and 

 behind the last arch there is the ordinary fissure; a 

 respiratory gill lines the opercnlum, and a pseudo- 

 brancliia is also present. The branchiostegous mem- 

 brane passes without division eveidy across the throat, 

 and is sustained on each side by three branchios- 

 tegals. The swim-bladder is divided into cells, the 

 partitions being provided with muscles; and the pneu- 

 matic opening is a long slit in the upper wall of the 

 tlu'oat. The stomach has no CiEcal expansion ; there 

 are several pancreatic ca;ca ; and there is uo spiral 

 valve in the largo intestine. AD the fins are protected 

 on their proximal edges by two rows of spinous scales, 

 and are supported by jointed rays only. Tiie hetoro- 

 ccrcal caudal is abru]3tly truncate, its rays being inserted 

 partly at the extremity of the vertebral column, partly 

 beneath it. The upper jaw and mandible are closely 

 set with raduliform teeth, bordered by a row of larger 

 pointed ones. The Lcpidostids have no blowing-holes 

 like those of the Sturgeons and Polypteres. 



Family II.— POLYPTERIDS (Pohjptcridw). 

 Plate 14, fig. 71. 



This is an African family hitherto detected only in the 

 Nile, Senegal, and Tchadda or Niger. It is equivalent 

 to MuUer's group of Puhjiittrini, and is not considered 



to be a less characteristic representative of the Ganoids 

 than the Lcpidostids. Polypterus, the only genus, 

 consists of three species closely resembling each other. 

 They are elongated fishes, with blunt depressed snouts, 

 having their heads protected by bony plates— somewhat 

 similar to the cephalic plates of the Sturgeons — and 

 their backs furnished with an even row of detached 

 fiiilots, each having a strong spine in iront, followed by 

 four or five soft branching rays. The caudal, bluntly 

 rounded, embraces the acutely conical end of the tail, 

 and comes farther forward on the dorsal aspect than it 

 does below. Tlie anal is situated immediately before 

 the lower lobe of the caudal, and the ventrals are behind 

 tlie middle of tlie fish. These are supported in front 

 by scaly bases, and tlie pectorals have still more con- 

 spicuous scaly bases resembling short arms. The 

 scales which closely envelope the body arc very strongly 

 adherent, stout, and very hard. 



In this family the upper jaw is not divided by a 

 longitudinal cleft as in the Lcpidostids ; and the man- 

 dible and skull generally, are constructed as in the 

 osseous fishes. A labial cartilage situated at the corner 

 of the mouth sup[)orts the upper and lower lips. Tlie 

 nostrils are more complicated than in other fishes, 

 as they consist of a large labyrinth of five passages, 

 each having a gill-like folding of the lining membrane. 

 The anterior nostril is prolonged into a membranous 

 tube ; the posterior opening is a small cleft before tlic 

 eye. The fourth gill is unifoliate only ; there is no 

 opercular giU; no pseudobrancbia; and no inferior pha- 

 ryngeal bones. The stomach is ca'cal ; there is a pan- 

 creatic ca;ciim ; and the large intestine is furnished witli 

 a spiral valve. The air-bladder consists of two sacs of 

 diflerent lengths, opening into a short common cham- 

 ber, which communicates by a long gloltoid fissure 

 with the ventral floor of the gullet. A single gill- 

 opening on each side, has the common branchiostegous 

 membrane covered with a bony plate ; and there is also 

 a blowing hole on each side, furnished with an osseous 

 valve. 



The G'jmnarclius or chl-el-far of the Nile has a 

 lung-like air-bladder sujiplicd with venous blood. 



Order XI. — HOLOCEPH ALIDS. 



(Plate 15, figs. 75, 7G.) 



Passing by the Ccclocanth order as being wholly 

 fossil, we come to the Holocephali, containing the 

 single family group of Cuim^uids. These form a 

 passage to the Chondropterygians by the arrangement 

 of their gill-openinga. Like the Sturionidans, they 

 have only one external operculated opening on each 

 side ; but under the integument there is a common 

 canal proceeding from it, and receiving the four 

 branchial slits. The complete biserial gills are attached 

 by their margins, and are only three in number; but 

 the inferior pharyngeal or fourth arch supports an 

 nniserial gill, and there is an accessory one on the 

 inner side of the operculum. There is a spiral valve 

 in the intestine, and there is no swim-bladder. The 



long, muscular, arterial stem is provided with three 

 rows of valves. Placoid granules exist in the integu- 

 ment, but the internal skeleton is cartilaginous, with 

 partial and scanty bony deposits. Most of the fins aie 

 supported in front by a strong spine, and the ventrals 

 are situated on the belly. 



The u]iper jaw is represented by the vomer, pala- 

 tines, and tympanals, in a rudimentary state, on the 

 sides of the snout ; and the function of teeth is per- 

 formed by four hard, bony plates above and three 

 below. The males are provided with trifid appendages 

 named " claspers ;" and tlie eggs of the females are 

 large and leathery or horny, with flat velvety borders. 



The genera are — Chimara (British) and Callorhynchus. 



