26 HOCENE MOLLUSCA. 
horizontal. This arrangement of the lamine is well displayed in fig. 14, Tab. I, drawn 
from a specimen found at Sheppy, for the use of which I am indebted to Mr. Dixon, 
to whom it belongs. The ventral margins of the laminz extend quite across the 
connecting plate before mentioned; and on each side, at a short distance from the 
extremities, they expand into the lateral portions of the laminz, small projecting frag- 
ments of which are sometimes still found adhering to the sides of the sheath. It is 
evident from this that the opinion expressed by M. Voltz, that there existed in each of 
the laminze an opening placed near the ventral margin, is correct. These openings 
appear to have been of an elliptical form, with their shorter axes in a line from the 
ventral to the dorsal surface, and were lined with an extremely thin calcareous sheath, 
which extended throughout the whole series of the laminze, and of which portions are 
frequently found adhering to the immer edges of the ventral margins and the lateral 
fragments of the laminee. This sheath corresponds with the siphon of the Belemnites, 
and is represented in the Sepion by the calcareous layer which, extending over the 
posterior edges of the lamine, covers the entire surface of the last lamina, and it 
presents, as M. Voltz states, an intermediate form between the narrow, straight siphon 
of the Belemnites and the wide, open cavity of the Sepion. 
Whether the spaces between the laminz were filled with minute columnar partitions, 
similar to those which characterise the Sepion, or whether they were simple air- 
chambers, we have not at present any evidence to determine. The probability is, that 
they were simply air-chambers; for no trace whatever of any substance similar to that 
termed the spongioid tissue of the Sepion has been found, which, had any such 
substance existed, might reasonably have been expected; and the true siphonal 
structure, to which the Belosepion presents so close an approximation, is always 
associated with simple air-chambers. ‘The Belosepion, as its rostrum indicates, be- 
longed to a Cephalopod eminently littoral in its habits, and the size, notwithstanding 
the extraordinary development of the rostrum, leads us to believe that the animal was 
not only smaller, but a less powerful swimmer, than the recent Sepia. We should 
expect, therefore, to find in it some provision for buoyancy beyond that with which 
the recent Sepia is furnished, not only for the purpose of increasing the swimming 
power of the animal, but also as a compensation for the large and dense rostrum and 
callus which characterise its remains. But if the interlaminar spaces were filled with 
any substance resembling the spongioid tissue of the Sepion, the floating apparatus of 
the Belosepion would be apparently inadequate to the wants of the animal. The form 
and mode of superposition of the laminz, somewhat resembling the arrangement of 
the septa in Spirulirostra, present a closer analogy with the phragmocone of the 
Belemnites than with the plates of the Sepion. These considerations give additional 
weight to the opinion of M. Voltz, founded on the appearance of what he terms the 
“alveolar sutures,” that the Belosepion was a camerated and siphoniferous shell. 
The rostrum of the Belosepion presents a structure analogous with that of the 
