40 EOCENE MOLLUSCA. 



The principal character, however, which distinguishes Belemnosis is the aperture 

 forming a communication between the alveolar chambers and the sac in which the 

 shell was lodged. In all the camerated siphoniferous shells, I believe without exception, 

 the inferior extremity of the alveolus and phragmocone is perfectly closed, and the air- 

 chambers have not any direct communication with the pallial sac ; and, in fact, commu- 

 nicate only with the pericardial cavity by means of the membranous siphuncle. Walch, 

 it is true, in his ' Recueil de Monumens, &c.,' figured a Belemnite, which he described as 

 having a small circular hole at the extremity of a curved point ; upon which figure, 

 with embellishments of his own, De Montfort proposed the genus Paclites, referred to 

 by Parkinson, and quoted by De Blainville. This genus, however, is universally 

 rejected, as founded on characters merely accidental or imaginary. M. d'Orbigny 

 states, that in certain exceptional cases the extremities of the rostra of Belemnites, at 

 the last period of their growth, form tubular prolongations, and that they are also liable 

 to distortion from accident. The extreme points of the successive layers, which form 

 the spathose guard, are apparently, in some instances, more susceptible of disintegration 

 than the other parts, and thus tubular openings may be formed along what Voltz terms 

 the apicial line. But in all these cases the pore is merely terminal, and does not 

 extend far up the sheath. The structure found in Belemnosis, therefore, appears to 

 be peculiar to it ; and would indicate an application of the siphuncular function, 

 whatever that function may be, different from that in all other siphoniferous shells, 

 and suggests a corresponding peculiarity in the organization of the animal. 



From the absence of the elongated rostrum which characterises the Belosepia 

 and Belopterce, we infer that the animal of Belemnosis was not littoral in its habits, 

 but existed in a comparatively deep sea ; and the occurrence of the unique 

 specimen, upon which the genus is founded, at Highgate, where the organic remains 

 indicate a shallow-sea deposit, is attributable most probably to the casual drifting of 

 the animal. 



No. 6. Belemnosis plicata. F. E. Edwards. Tab. 2, fig. 3a — e. 



Beloptera anomala ; Sowerby. 1829. Min. Con. vol. vi, p. 183, tab. 591, fig. 2. 



— — Morris. 1843. Cat. of Brit. Foss. p. 1/8. 



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



— — Deshayes. 1845-6. 2d Edit, de l'Hist. Naturelle, &c. par Lam. 



— — D'Orbigny. 1845-7. Moll. viv. et foss. torn, i, p. 309, tab. 14, 



figs. 8-10. 



B. testa oblong o-elongatd, supra convexd, umbone obtusissimo, lateraliter compresso, 

 et deorsum leviter inrfecto terminatd : marginibus ventralibus antice depressis, posiice 

 sub-convexis, fades externas acutas, internas, oblique triplicatas, prcebentibus : foramine 

 umbonali circulari. 



