PROFESSOR OWEN ON THE 13ELEMNITE. 
69 
this must have belonged to an animal just excluded from the egg, if excluded at all. 
The layers of growth immediately added to this axis extend beyond it, both anteriorly 
and posteriorly ; and, being thicker in the middle than at the two extremities, render 
the guard fusiform, as in the young specimen rather more than an inch in length* 
from the same stratum and locality as the preceding. At this stage of growth, which 
lasts longer in some species, as the Belemnites subfusiformis , than in others, the 
spathose guard has been mistaken for the spine of an Echinus, and this idea, first 
entertained of Belemnites in general by Klein, has been reproduced in later times 
by M. Raspail: even the sagacious Mr. Miller-^, who has done so much towards 
the elucidation of the Belemnites, was led to conceive the fusiform guard of imma- 
ture individuals to be remains of a distinct genus, for which he proposed the name 
of Actinocamax\. 
The exterior surface of the spathose guard of the Belemnites of the Oxford clay, 
though smoother than in some other species, is minutely granular, and occasionally 
presents faint traces of vascular impressions, proving it to have been invested by an 
organized membrane of the living Cephalopod. On two specimens from this con- 
servative stratum, I have detected remains of a more immediate investment of a thin 
friable layer of white calcareous matter, analogous to that of the outer layer of the 
sheath of the phragmocone. The animal membrane or constituent of the spathose 
guard has been alluded to by Dr. Buckland as being evidenced by the odour 
resembling burnt horn, produced on burning this part of the Belemnite. I will only 
add in reference to the spathose calcareous constituent, that its microscopic struc- 
ture proves it to be an original formation, deposited in membranous cellular moulds, 
under the influence of the vital organizing forces, and not to be the result of 
post-mortem infiltration of mineral substance, into an originally light and porous, 
or cellular texture, as Walch, Parkinson, Lamarck and De Blainville§ have 
conjectured. 
As respects the phragmocone and its investing sheath, the well-preserved Belem- 
nites of the Oxford clay demonstrate that the sheath is continued backwards to line 
the alveolar cavity of the spathose guard, as well as forwards from its basal outlet 
to form the visceral chamber anterior to the phragmocone. The phragmocone in 
these specimens appears broader than it actually was on account of the compression 
* PL II. fig. 5. 
t His conjectural figure of the recent Belemnite (Geological Transactions, new Series, vol. ii. (1826) PI. IX. 
fig. 15) is essentially the same with those which have been since published by Dr. Buckland, M. D’Ohbigny 
and M. Duval-Jouve. 
+ M. Duval (Mem. sur les Belemnites, 4to, 1841, p. 68) has demonstrated, what MM. De Blainville and 
D’Orbigny suspected to be, the true nature of the Actinocamax of Miller. 
§ Sur les Belemnites, 4to, 1827, pp. 32, 33. Specimens of the spathose guard have been discovered which 
have been fractured during the life-time of the Belemnite, and healed ; the broken portions having been 
held together by the surrounding organized integuments, and reunited by the deposition of new layers of the 
fibrous structure peculiar to the guard. Duval-Jouve, Sur les Belemnites, p. 37, PI. X. 
