66 
PROFESSOR OWEN ON THE BELEMNITE. 
of the shell, which is usually the only part preserved, and now extended in its appli- 
cation to the entire animal. 
2nd. The chambered or siphonated part of the shell which I have called the 
1 phragmocone*,' and which is lodged in the conical alveolus or cavity at the base of 
the ‘ guard.’ 
3rd. The conical, thin, but dense, corneo-nacreous case-f-, which immediately in- 
vests the phragmocone, and lines the alveolus of the guard ; commencing at the 
bottom or apex of that cavity, and continued beyond the thin margins of the basal 
aperture of the alveolus, and beyond the last septum of the phragmocone, to form, as 
Dr. Buckland rightly describes^, the large anterior chamber of the Belemnite con- 
taining the ink-bag and some other viscera. 
The numerous species of Belemnite have been classified according to the modifica- 
tions of the spathose guard ; the one under consideration belongs to the group cha- 
racterized by a rounded, elongated, conical guard, with a short, terminal, ventral, 
longitudinal impression ; it was first recognised as a new species by Mr. Pratt, who 
has honoured me by naming it Belemnites Owenii. This species approximates in its 
general form to the Belemnites elongatus and Bel. longissimus of Miller, from the 
lias ; but it presents intermediate proportions of length to breadth, and maintains the 
same diameter throughout a much greater part of its extent ; the anterior expansion, 
which is very gradual, commencing, nevertheless, nearer the alveolar extremity, and 
ending less widely. The excavated part of the guard becomes very thin as it ex- 
pands, and, there having been no infiltration of mineral matter into its cavity, 
or into the chambers of the phragmocone, it has yielded to the pressure of the super- 
incumbent strata, and thus in its flattened and fractured state shows a greater 
degree of expansion than is natural to it. The thin and brittle margin of the 
spathose alveolus may be traced nearly half way towards the base of the phragmo- 
cone, which is there invested only by the thinner and more yielding corneo-nacreous 
sheath §. 
The gradual expansion of the guard from its posterior end or apex is shown in the 
figure 1. The ventral groove (fig. 2 a') extends to about one-fourth the length of the 
guard, commencing a little in advance of the apex : it is very shallow, with the 
* PI. II. figs. I c, 6,7 and 8. <1 >paypos partition, kwyos cone. Lectures on Comparative Anatomy, 8vo, 1843, 
p. 333. The term ‘ alveolus’ has usually been applied to the chambered cone ; but it appears better to restrict 
it to the socket in which the chambered cone is lodged. 
f PI. II. fig. 6, and fig. 7, r t . 1 Bridgewater Treatise, 1836, p. 372. 
§ In the specimen of Belemnites elongatus figured by Miller (Geol. Trans. 1826, PI. VII. fig. 6.), this thin 
sheath, which extends beyond the wider part of the alveolus, had perished, as is usually the case, and the casts 
of the chambers of the phragmocone, which is preserved in situ, are exposed. To this is due the appearance 
which M. De Blainville was unable to understand in the figure above cited. “ Ce que je ne conqois pas 
dans cette figure, e’est la maniere dont les calottes empilees, qui constituent P alveole, depassent de beaucoup 
la cavite de la coquille ou du tube, dont les bords sont cependant assez amincis pour croire que le peristome 
est parfait.” — Sur les Belemnites, p. 95, 4to, 1827. 
