192 DESCRIPTION OF SHELLS. 
the sac, and have had muscles to move them attached to the shell and working 
against its sides. On the ventral surface the cavity opposite the dorsal ridge or 
callus is deep and conical, and surrounding it are the remains of thin plates or 
septa, running obliquely to the slightly curved axis of the cavity, across which 
however they did not reach, but had their edges reflected against each other. 
There are no indications of thin tortuous laminz between them, so that as far as 
we can at present tell, they are equally unlike the septa in Belemniies and the 
spongy mass in Sepia. The cavity is enclosed on the ventral side by a flat plate 
or diaphragm ; the space between it and the reflected edges of the septa has been 
thought to represent a siphon. In general only the calcareous portions are pre- 
served ; and if the spine and posterior extremity were ever covered by a horny 
coat, it has entirely disappeared. In one specimen from Sheppy, for which we 
are indebted to Professor Owen’s kindness, there are indications of the internal 
membrane between the calcareous coats, the animal matter being displaced by 
pyrites. This specimen is filled with indurated marl or cement stone, and is much 
longer than any other we have seen, but shows very slight marks of septa, which 
probably did not extend far from the apex, or may have been only narrow rudi- 
mentary rings*. The following short description may serve at present to define 
the genus :— 
Gen. Cuar.—Animal probably a dibranchiate Cephalopod ; shell internal, 
membranaceo-calcareous, elongated, very concave, its posterior extremity keeled, 
and rugose on the back forming a callus, compressed on the sides, and the 
ventral plate expanded, striated, thickened, and toothed at the terminal edge; a 
strong spine is placed between the extremity of the dorsal keel and the ventral 
plate ; ventral cavity enclosed by a flat longitudinal plate or diaphragm, and con- 
taining many thin oblique septa ; anterior portion thin, rounded, concave beneath. 
The species are probably numerous, but they are extremely difficult to define, 
as age and other circumstances to which internal shells are particularly liable 
appear to cause much variation. They all occur in the same tertiary forma- 
tion ; the following, from Bracklesham, are supposed to be new. 
* Tab. IX. fig. 17, (a) the outer dorsal calcareous coat; (4, 6, 6) two or three imbricating layers of 
membrane alternating with calcareous lamine; (c, ¢) the calcareous lining; (d@) the surface of the 
stone waved in the direction of the lines of growth or margin of the shell; (€) a portion of the dia- 
phragm; (f) the abraded surface of the beak or spine, showing a fibrous structure not visible in Sepia ; 
(a) a portion of the diaphragm, also shown at (g) in figs. 12 & 16; (4) striw indicating a fibrous 
structure under that part of the surface where I suppose a muscle to have been attached. 
