CEPHALOPODA. 30 



species but also the Beloptera anomala of Sowerby to the genus Beloptera, the 

 principal character of which he states to be the association of a conical chambered 

 cavity, similar to that of the Belemnitcs, with the beak (rostrum) of the Sepia. M. 

 d'Orbigny also (Moll. viv. et foss.) refers to that genus the remains in question, which, 

 he says, resemble Bcloptera Levesquei in the absence of the lateral wings, but are 

 distinguished from it as well by the want of the under part (the ventral paries) of the 

 shell and of a distinct beak, as by the air-chambers being apparent on the under side. 

 These remains unquestionably bear a close affinity to Beloptera ; but the peculiarities 

 they present appear to me to separate them distinctly from that genus, and fully to 

 justify the establishment of a new genus for their reception. 



The shell of Belemnosis consists of an elongated semiconical sheath, the apex 

 of which expands into a short semicylindrical umbo, pierced on the ventral surface, 

 and inflected towards the ventral aspect. The sheath is convex on the dorsal surface, 

 and is without a ventral paries ; the margins at the superior extremity are narrow, 

 and present outwardly sharp edges, which extend rather more than one third of 

 the length of the shell ; as the margins approach the inferior extremity they expand, 

 and the inner edges gradually become nearer to each other, until they unite immediately 

 above the umbonal pore. The margins of the pore are elevated, and the pore itself 

 penetrates to, and communicates with, the air-chambers. The septa are transverse 

 and concave ; the presence of a siphuncle and its ventral position are indicated by 

 angular inflections on the sutural impressions along the medial line of the ventral 

 surface ; the septa are contained in, and wholly enveloped by, a thin conical sheath, 

 which also is covered by a second and somewhat thicker conical layer lodged in the 

 outer sheath. 



The principal character of Beloptera, viz., the association of the elongated rostrum 

 of the Sepion with the phragmocone of the Belemnite, fails in Belemnosis ; and the 

 lateral expansions which, assuming their fullest development in Beloptera Belemnitoidea, 

 still characterise B. Levesquei, although reduced in that species to prominent carinas, 

 are here wanting, or, at the utmost, are but feebly represented by the sharp outer 

 edges of the ventral margins of the sheath. In Beloptera, the outer cone, which 

 contains the inner sheath and its contents, and which exactly corresponds with the 

 phragmocone of the Belemnite, is entire ; whereas, in Belemnosis, the ventral paries 

 is wanting, or very thin. In this respect Belemnosis presents an analogy with Belem- 

 nitella (D'Orb.), a genus of the Belemnitidse, characterised by a fissure in the phrag- 

 mocone communicating with the external paries of the alveolus. This peculiar form of 

 Belemnite at present appears to be confined to the upper chalk formation, and it would 

 seem to connect the true Belemnite with the present genus, in which the fissure be- 

 comes largely expanded, resembling the wide cavity of Belosepia. Thus the transition 

 from Belosepia, through Belemnosis and Belemnitella, into Belemnite will be easy and 

 natural, and the chain of connexion between the latter genus and the recent Sepia will 

 be complete. 



