CEPHALOPODA. | LOWER PALAZOZOIC MOLLUSGA. 307 
ist Ord. Trrraprancniara (Owen). 
= Tentaculifera (dOrb.) 
Body without fins, always contained in an external shell, to which it is fixed by two large lateral muscles, 
and a narrow horny cincture to the abdominal part of the mantle. The septa are pierced by a siphuncle con- 
taining a tubular prolongation of the mantle; anterior edge of the mantle thickened and divided into several 
lobes, one semicircular dorsal fold resting against the inrolled spire, one triangular hood-shaped flap covering 
the back or top of the head, and a large number (seventeen to nineteen on each side in Nautilus) of lobes, 
bearing numerous, short, transversely crenulated, slender tentacles ; the eyes large, but projecting on peduncles, 
as in the Gasteropoda, and with a short tentacle before and one behind each, analogous to the four tentacles of 
some Grasteropods in position and origin of the nerves ; there are also four labial processes with a large number 
of labial tentacles, like those of the mantle; cranial cartilage confined to the under side of the head, having a 
groove on the upper surface to support the annular brain, and giving off processes of attachment to the muscles 
of the funnel, and the lateral adhering muscles. Funnel slit along the ventral aspect, strongly contractile, with 
a valve at the opening. The nervous collar is stirrup-shaped, the supra-cesophageal portion very thick and 
simple, enlarging at the ends, and giving off twigs to the eyes, and lower tentacles of the eyes, and muscles 
of the mouth; the inferior portion double, the anterior inferior semi-ring giving twigs to the tentacles; the 
posterior one giving off flattened twigs to the muscles of the shell, a set of slender twigs to the stomach, 
and two long respiratory branches each with a ganglion at the base of the gills, which twigs go to the 
heart, &c.; the posterior semi-ring is therefore the analogue of the pedial and branchial ganglia in the 
lower mollusca. The dorsum of the tongue is armed with a horny coat, covered with recurved hooks; the 
cesophagus, after passing through the neural collar, dilates into a large crop, which contracts to a slender 
tube before entering an oval gizzard, from which the intestine extends, with first an abrupt backward and 
then forward bend, to terminate in the branchial cavity, at the base of the funnel; near its origin is a round 
laminated biliary appendage or pancreas, receiving the bile from the ducts of the lobulated quinquepartite 
liver, which is large, extending from the crop to the gizzard; no ink-gland. The pericardium contains the 
dilated end of a vena cava, taking the venous blood from the head, mouth, tentacles, and funnel, &c., and 
sending it to the two pairs of gills, by four branches, to which are clustered a number of (?) renal glands ; 
each vein at the base of the gill having a valve to prevent the return of the blood; beyond this valve the yessel 
becomes the branchial artery, ramifies through the gill, ending in a branchial vein for each gill, taking the 
aerated blood to the four corners of a transversely oblong systemic ventricle, which gives off an anterior and 
a posterior aorta—the former small, supplying the nidamental gland, and extending backwards through the 
siphon ; the latter large, with a muscular bulb at its origin supplying the body. The females have an ovary 
on the right side of the gizzard, the oviduct running beside the intestine, and terminating near the anus. 
In advance of the termination of the oviduct is a pair of (?) nidamental glands (as in the Pectinibran- 
chiate Gasteropods), for adding the shell and connecting substance to the eggs. 
The formation of each septum begins at the circumference and extends to the siphuncle, which it extends 
over backwards ; the penultimate chamber is smaller in the adult than the preceding ones. The shell of the 
embryo Nautilus is simple and unchambered. 
The apparent absence of an ink-bag induces Prof. Owen to class the Ammonitide with the Nautilide. 
The order contains three families :—1st, Bellerophontide ; 2nd, Nautilide ; 8rd, Ammonitide. 
Ist Family. BELLEROPHONTID& (d/°Coy). 
Shell thick, spirally inrolled, monothalamous ; a defined siphonal band on the circumference (as in Argo- 
nauta) ; usually a distinct inner lip overspreading part of the inrolled spire, deposited by a dorsal flap of the 
mantle (as in Nautilus). 
RR2 
