CEPHALOPODA. 37 



lateral expansions are inclined towards the ventral aspect, and give a convex form to 

 the dorsal surface, and a corresponding concavity to the ventral surface ; they 

 are thick at the juncture of the rostrum and sheath, and become gradually thinner as 

 they enlarge, presenting a sharp cutting edge on their free outward margins. In this, 

 the typical species, they are largely developed, regular in form, and vary considerably 

 in size according to the age of the individual ; in young specimens they present an 

 elongated semielliptical form, which, as the shell advances towards maturity, becomes 

 nearly semicircular. 



Figs. \f and \g represent a variety in which the inferior cone is shorter, broader, 

 and more compressed, and the wings are wider than in the ordinary specimens. 



The B. Bdemnitoidea is found in England at Bracklesham Bay, where it is some- 

 what rare. In France it is found in the nummulitic bed at Biaritz, in the Lower 

 Pyrenees ; the lower beds of the calcaire grossicr at Vivrais, Grypseuil, and Pouchon 

 (Oise), and, in the middle beds, at Grignon, Parnes, Muchi-le-Chatel, Chaumont, &c. 

 It also occurs in Belgium, in the sandy beds at Laeken. 



The size is eleven lines in length, and four lines and a half in width across the widest 

 part of the lateral expansions. 



No. 5. Beloptera Levesquei. UOrbigny. Tab. 2, fig. 2a — e. 



Beloptera Levesquei ; D'Orb. et Fer. 1839. Cephal. Acetab. Seiches, tab. 20, figs. 10-12. 

 — — Pictet. 1845. Traite element, de Paleont. vol. ii, p. 316. 



B. testa oblongo-elongaid, arcuatd, subtus carinatd, lateribus depressd, sub-excavatd ; 

 antice cyli?idrico-angustatd : rostro obtuso, striato : appendicibus lateralibus parvis, 

 linearibus. 



Shell elongated, arched : the sheath straight and nearly cylindrical ; the ventral 

 paries thickened, and laterally much compressed, so that, instead of the flat square- 

 shaped, bifurcating ridge which distinguishes the preceding species, it presents along 

 the middle of the sheath, beneath the siphuncular line, a somewhat acute angular keel, 

 which is continued on the upper part of the rostrum, and the sides of which are a 

 little depressed. The rostrum itself is larger, and is transversely more compressed, 

 and less inflected towards the ventral aspect, than that of B. Bdemnitoidea. 



M. d'Orbigny describes the species as destitute of lateral expansions ; but, in the 

 figures given by him, there are unquestionable indications of those appendages, very 

 slightly developed it is true, yet still representing the wing-shaped expansions which 

 characterise the genus. In one of the two English specimens, the only two with which 

 I am acquainted, and for the use of which I am indebted to Mr. Wetherell, the lateral 

 expansions are broken away, but their existence is evidenced by a deep suture on each 

 side where they were inserted into the shell. The other specimen unfortunately is 

 broken off just above the juncture of the sheath with the rostrum, at the precise part 



