MANUAL OF THE MOLLUSCA. 
fessor Owen describes the fibres, in specimens from Christian 
Malford, as of a trihedral prismatic form, and zoooth of an inch 
in diameter. These fibres are disposed concentrically around 
an axis, a, the so-called apical line, which extends from the 
extremity of the phragmocone to that of the rostrum. Indica- 
tions of a thin capsule or formative membrane appear in some 
Belemnites investing the guard; in those of the Oxford clay 
it is represented by a granular incrustation; in some lassic 
apecies it appears in delicate plaits, hke ridges or furrows; In 
some specimens of Belemnitella mucronata from the upper chalk 
of Antrim, it is in the form of a very thin nacreous layer. 
- 3. A pro-ostracum, or anterior shell, which is a dorsal exten- 
sion of the conotheca beyond the end where the guard disappears. 
[The surface of the conotheca is marked by lines of growth, 
and, according to Voltz, it may be described in four principal 
regions radiating from the apex: one dorsal, Fig. 2, a, with 
—— Se 
———S—== SS 
—SS SS" 
SS 
=~ 
se 
SSS 
AS 
—— 
= 
——— 
— 
—S 
== = 
SSS 
SS 
Fig. 2. Fig. 3. Fig, 4. 
loop lines of growth advancing forward; two lateral, b, separated 
from the dorsal by a continuous straight or nearly straight line, 
and covered with yery obliquely arched striz in a hyperbolic 
form, in part nearly parallel to the dorso-lateral boundary line, 
and in part reflexed, so as to form lines in retiring curves across 
the yentral portion nearly parallel to the edges of the septa. 
4 
