28 EOCENE MOLLUSCA. 



into an elevated mass towards the middle ; while in Belosepion, after emerging from 

 the terminal cavity, in 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 laminae become more and 

 more distant, and the laminae themselves tend gradually towards a horizontal position ; 

 and in fact, in an adult individual, the last laminae become nearly horizontal. 



Owing to the different mode of arrangement of the laminae, 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 laminae ; but in the Sepion, the laminae 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 Belosepion, in which the 

 laminae, being vertical, or more or less vertically inclined, present to it merely their 

 dorsal and lateral margins. The buckler of the Sepion, 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 Belosepion 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 laminae, 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 laminae 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. Yoltz. I have, 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 Sepia, 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 Scpidce, in which M. d'Orbigny has placed it, to the family Belemnitidae. 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 Bclemnitella 

 and Belemnite. 



