106 BRITISH BELEMNITES. 
Betumnirus Bessinus, D’Orb. Pl. XXVI, fig. 63. 
Reference. B. Bessinus, D’Orb., ‘ Pal. Frang. Ter. Jur.,’ p. 110, pl. xin, figs. 7—13, 
1842. 
B. canaliculatus, Quenst., ‘Ceph.,’ p. 438, pl. xxix, fig. 7, 1849. 
Guarp. Elongate, gently and equally tapering till near the apex, which is subacute ; 
depressed in all the post-alveolar and part of the alveolar region, nearly circular in the 
advanced part of the alveolar region; ventral surface marked by a deep distinct groove 
reaching from near the apex to about the last or most advanced of the septa im the 
phragmocone. 
‘Transverse section nearly circular at the alveolar apex, much depressed in all the 
region behind it. 
Dimensions. Greatest length observed 6;, inches (specimen in Oxford Museum) ; the 
alveolar cavity occupies 1} inch. Diameter at alveolar apex 0°6 inch. 
Proportions. Taking the diameter v d at the alveolar apex = 100, that from side to 
side = 105; the axis is excentric and = 500; near the apex the diameter from side to 
side is to that from back to front as 135 : 100. 
Puracmoconn. In several specimens this part of the Belemnite shell is seen; in one 
of my examples it is very well seen. The angle is from 18° to 29°; the sides are straight ; 
the back and front very slightly curved; the apex is a spherule; the septa are at the 
ordinary distance—about one sixth of the diameter; the axis of the chambered part 
visible is half the length of the axis of the guard; the diameter of the largest septum 
(crushed) } inch. But single septa occur in the Stonesfield strata which measure | inch 
across, and are very nearly circular. 
Locality. Stonesfield, Oxfordshire, in the lowest fissile beds of the Great Oolite. 
Observations. The specimens which are represented in Pl. XX VI under the name of 
B. Bessinus, agree very fairly with D’Orbigny’s figure already referred to, except 
that no trace of contraction in breadth appears about the alveolar apex, as in his example, 
giving a slightly subhastate figure to the guard. But a specimen in the Oxford Collec- 
tion, of the same size as the largest of our figures, exhibits this peculiar outline in a very 
slight degree; it also shows, but not very clearly, the double shallow stria which is 
mentioned at the retral extremity of the deep, well-defined ventral groove (D’Orb., pl. xi, 
fig. 7). If to these points of agreement we add the conformity of the angle of the 
phragmocone (20° in each), there will be little reason to doubt the agreement of the species. 
D’Orbigny obtained his specimen from the Inferior Oolite of Port-en-Bessin (Calvados). 
