394 
' DR. MANTELL ON THE BELEMNITE. 
beyond the upper or basilar margin of the phragmocone is well defined ; and in each 
of these specimens the extension of the longitudinal plates or bands maybe distinctly 
traced downwards, almost to the distal end or apex, as a thin nacreous shelly plate, 
striated longitudinally, and having obliquely divergent lines on the ventral margin. 
The finest specimen from Wiltshire in the British Museum (Plate XXVIII. fig. 1), like 
that discovered by my son*, consists of the osselet or guard {h) partially invested by 
its capsule, with the phragmocone in natural apposition ; the latter is shattered and 
pressed almost flat, but preserves a conical outline, and has on the upper part the 
right process (e), which extends 5 inches above the peristome or border of the cham- 
bered cone ; a portion of the left process is seen at f; c, denotes the lower termination 
of the process. 
Fig. 2 represents the upper portion of this fossil of the natural size, and so clearly 
shows the parts described that further detail is unnecessary. 
I would particularly direct attention to the evident extension of the base of the 
process {x, x, x) down the phragmocone as a nacreous band or plate finely striated. 
Under a slightly magnifying power this expansion appears like a thin shelly integu- 
ment deposited on the external surface of the chambered cone, and is marked with 
curved diverging lines on the lateral border. 
In the former Memoir the number and position of these processes could not be 
determined with precision ; the specimens recently obtained show that there were 
but two, — one on each side the aperture or peristome, — and these were situated nearer 
to the dorsal than to the ventral aspect. Thesiphimculus always occupies the median 
and ventral side of the phragmocone ; and its excentric apex is directed towards the 
same region, in which is also situated the sulcus of the guard (see Plate XXIX. fig. 5). 
In the fragment of a large uncompressed belemnital phragmocone from Lyme 
Regis, for the loan of which I am indebted to Mr. Morris, the relative position of 
the parts above described is distinctly exhibited, Plate XXIX. : fig. the remains 
of the lateral processes ; g, the siphunculus, occupying the ventral aspect ; h, the 
dorsal line. 
The outline, Plate XXIX. fig. 4, is intended to express concisely the facts described. 
With regard to the osselet (the distal solid part of which is generally termed the 
guard or rostrum), I would remark, that since my former communication I have in- 
spected many hundred specimens from various localities, and have ascertained that 
although in detached examples (the ordinary condition in which these fossils occur) 
the rostrum appears to terminate by a well-defined line at the upper part, yet this is 
not really the case ; for the same radiated structure originally extended upwards, 
and surrounded and protected the phragmocone as a sheath, and gradually became 
confluent with the investing capsule or periostricum ; probably terminating in a 
horny flexible integument. A fragment of the receptacle taken from the upper part 
of a specimen, and which is not thicker than stout paper, is delineated under a mag- 
* Philosophical Transactions, 1848, Plate XV. fig. 3. 
