28 EOCENE MOLLUSCA. 
into an elevated mass towards the middle ; while in Belosepion, after emerging from 
the terminal cavity, m which they radiate, as it were, from the origin of the fold, they 
are at first nearly vertical, with the edges of the ventral margins ranged in a line with 
the ventral surface of the rostrum, and converging towards the inverted apex of the 
sheath ; so that, as the sheath enlarges, the dorsal edges of the laminze become more and 
more distant, and the laminz themselves tend gradually towards a horizontal position ; 
and in fact, in an adult individual, the last laminz become nearly horizontal. 
Owing to the different mode of arrangement of the lamin, the Sepion and 
Belosepion differ materially in their shape and general aspect. In each the dorsal plate 
or sheath is extended so as to embrace the laminz ; but in the Sepion, the lamine of 
which are horizontal, and placed in a direction nearly parallel with the sheath, it is 
necessarily much less convex and more extended than in the Pelosepion, in which the 
laminze, being vertical, or more or less vertically inclined, present to it merely their 
dorsal and lateral margins. The buckler of the Seyzon, and its contents, are, therefore, 
in form an elongated oval, depressed in the direction from the ventral to the dorsal 
aspect, and but slightly convex on the surfaces; while in the Be/osepion the sheath is 
considerably shorter, enlarging gradually towards the anterior extremity, and presents 
a deep semiconical cavity, containing within it the whole area of the lamine, and it is 
obliquely truncated at the anterior extremity, and flat on the ventral surface, which 
does not extend to half the length of the shell. The most important difference, however, 
is, that the laminz of the Belosepion possess large ventral, siphonal, or siphoniform 
openings, a structure which is not found nor represented in the Sepion. 
These distinctions indicate corresponding zoological peculiarities ; and the animal, 
although, perhaps, resembling Sepia more closely than any other recent Cephalopod, must 
yet have presented such marked differences from it as to render it impossible satis- 
factorily to refer its remains to that genus, and fully to justify the separation proposed 
by M. Voltz. Ihave, therefore, retained that author’s genus, Belosepia, notwithstanding 
the array of authorities against it; and I have the less hesitation in doing this, when I 
find that Cuvier did not refer the remains in question to Sep7a, but to some Cephalopod 
closely allied to that genus; and that M. de Blainville, when he adopted the genus 
Beloptera, did not hesitate to remove them from the genus Sepia, to which he had 
referred them, although he placed them, under some misapprehension, in the genus 
Beloptera. 
With respect to the place of Belosepia in the systematic arrangement, as the shell 
presents a camerated and siphoniform structure and a terminal guard, and is therefore 
more nearly related to Belemnite than the recent Sepia, I have removed it from the 
family Sepide, in which M. d’Orbigny has placed it, to the family Belemnitide. It 
seems to have prepared the way for the recent Sepia, and leads from that genus, 
by a natural and easy transition through Beloptera and Belemnosis, into Belemnitella 
and Belemnite. 
