1 62 Sauroids. FISHES. Polypterids. 
ing parts of Canada, wlierein about ten species have 
to be a less characteristic representative of the Ganoids 
been detected by Agassiz, and they are considered to 
than the Lepidostids. Polypterus, the only genus. 
be the nearest representatives now living of the extinct 
consists of three species closely resembling each other. 
ganoid fishes. 
They are elongated fishes, with blunt depressed snouts. 
In this family the upper jaw, which is elongated in 
having their heads protected by bony plates — somewhat 
the axis of the fish, is composed of several pieces ; and 
similar to the cephalic plates of the Sturgeons — and 
the mandible is also composed of many pieces, as in 
their backs furnished with an even row of detached 
the reptiles. The vomer is of two pieces, separated 
finlets, each having a strong spine in front, followed by 
by a median cleft. Instead of the first vertebra 
four or five soft branching rays. The caudal, bluntly 
being united to the occipital bone by opposing cups 
rounded, embraces the acutely cotilcal end of the tail, 
filled with an elastic gelatinous fluid as in ordinary 
and comes farther forward on the dorsal aspect than it 
fishes, that joint is formed by a hall and socket, so that 
does below. The anal is situated immediately before 
the head has a nodding movement. The olfactory 
the lower lobe of the caudal, and the ventrals are behind 
organ, situated at the tip of the upper jaw, contains 
the middle of the fish. These are supported in front 
the ordinary nasal folds arranged simply. The gills. 
by scaly bases, and the pectorals have still more con- 
on four arches, have a perfect bifoliate structure, and 
spicuous scaly bases resembling short arms. The 
behind the last arch there is the ordinary fissure; a 
scales which closely envelope the body are very strongly 
respiratory gill lines the operculum, and a pseudo- 
adherent, stout, and very hard. 
branchia is also present. The branchiostegous mem- 
In this family the upper jaw is not divided by a 
brane passes without division evenly across the throat, 
longitudinal cleft as in the Lepidostids ; and the man- 
and is sustained on each side by three branchios- 
dible and skull generally, are constructed as in the 
tegals. The swim-bladder is divided into cells, the 
osseous fishes. A labial cartilage situated at the corner 
partitions being provided with muscles; and the pneu- 
of the mouth supports the upper and lower lips. The 
matic opening is a long slit in the upper wall of the 
nostrils are more complicated than in other fishes. 
throat. The stomach has no ceecal expansion ; there 
as they consist of a large labyrinth of five passages. 
are several pancreatic caeca ; and there is no spiral 
each having a gill-like folding of the lining membrane. 
valve in the large Intestine. All the fins are protected 
The anterior nostril is prolonged into a membranous 
on their proximal edges by two rows of spinous scales. 
tube ; the posterior opening is a small cleft before the 
and are supported by jointed rays only. The hetero- 
eye. The fourth gill is unifoliate only ; there is no 
cereal caudal is abruptly truncate, its rays being inserted 
opercular gill; no pseudobran chia; and no inferior pha- 
partly at the extremity of the vertebral column, partly 
ryngeal bones. The stomach is cajcal ; there is a pan- 
beneath it. The upper jaw and mandible are closely 
creatic caecum ; and the large intestine is furnished with 
set with raduliform teeth, bordered by a row of larger 
a spiral valve. The air-bladder consists of two sacs of 
pointed ones. The Lepidostids have no blowing-holes 
dili'erent lengths, opening into a short common cham- 
like those of the Sturgeons and Polypteres. 
ber, which communicates by a long glottoid fissure 
with the ventral floor of the gullet. A single gill- 
Famii.y II.— polypterids {Polypteridai). 
opening on each side, has the common branchiostegous 
Plate 14, fig. 71. 
membrane covered with a bon^' plate ; and there is also 
a blowing hole on each side, furnished with an osseous 
This is an African family hitherto detected only in the 
valve. 
Nile, Senegal, and Tchadda or Niger. It is equivalent 
The Gymnarchus or del-el-far of the Nile has a 
to Muller’s group of Pulyptcviai, and is not considered 
lung-like air-bladder supplied with venous blood. 
Order XI. — HOLOCEPH ALIDS. 
(Plate 15, figs. 75, 76.) 
P.\s.siNG by the Coelocantb order as being wholly 
long, muscular, arterial stem is provided with three 
fossil, we come to the Holoce[)hali, containing the 
rows of valves. Placoid granules exist in the integu- 
single family group of Ciiimaskids. These form a 
ment, but the internal skeleton is cartilaginous, with 
jiassage to the ChondropteiTgians by the arrangement 
partial and scanty bony deposits. Most of the fins are 
of their gill-openings. Like the Sturionidans, they 
supported in front by a strong spine, and the ventrals 
have only one exteriial operculated opening on each 
are situated on the belly. 
side ; but under the integument there is a common 
The upper jaw is represented by the vomer, pala- 
canal proceeding from it, and receiving the four 
tines, and tympanals, in a rudimentary state, on the 
branchial slits. The complete biserial gills are attached 
sides of the snout ; and the function of teeth is per- 
by their margins, and are only three in number ; but 
formed by four hard, bony plates above and three 
the inferior pharyngeal or fourth arch supports an 
below. The males are provided with trifid appendages 
uniserial gill, and there is an accessory one on the 
named “ claspers ;” and the eggs of the females are 
inner side of the operculum. There is a spiral valve 
large and leathery or horny, with flat velvety borders. 
in the intestine, and there is no swim-bladder. The 
The genera arc — ChvtrKzra (British) and Callorhynchvs. 
