G. O. Crick—Actinocamax from the English Chalk. 393 
The posterior end is abruptly truncated at right angles to the axis 
of the guard, its ventro-dorsal and transverse diameters being 10 
and 12:5mm. respectively. The most inflated part of the guard is at 
a distance of 54 mm. from the alveolar extremity, and therefore only 
about 16mm. from the posterior truncated end; the ventro-dorsal and 
transverse diameters here are 12 and 13:5mm. respectively. It 
will thus be seen that in a ventral aspect the fossil has its greatest 
diameter at a point about three-fourths of its length from the alveolar 
end, and that from this point it tapers rather rapidly towards the 
alveolar end, but in the opposite direction only very slightly between 
this point and its posterior truncated end; whilst in a lateral aspect 
the dorsal and ventral surfaces are as nearly as possible parallel to 
each other. Anteriorly the fossil is compressed, whilst posteriorly it 
is depressed. The dorso-lateral grooves are well marked, and at 
about 6mm. below the alveolar border are only about 3 mm. apart ; 
in passing backwards they separate rather rapidly from each other 
until reaching the most inflated part of the guard, when they con- 
verge slightly over the rest of the specimen. Anteriorly each groove _ 
is flattened, broad, with its lateral boundary obscurely defined, and 
decreases in width rather rapidly until reaching the most inflated part 
of the guard, where it becomes relatively narrow (about 2mm. wide) 
and parallel-sided. The ventral surface of the posterior half of the 
guard is flattened. ‘The surface of the guard is smooth, but on the 
ventral portion of the most inflated part of the guard it is somewhat 
uneven, suggesting that here there is a slight deformation. 
Certain grooves and sharply-incised lines near the posterior end of 
the guard are evidently the marks of injury. Thus, on the ventral 
surface and towards the right side (see Fig. 2, A), and having its 
median line about 4 mm. from the posterior end, there is a transverse 
roughened groove about 7 mm. long and 4mm. wide, as if produced by 
a serrated edge. Also, on the right side and near the dorsal surface, 
there is another similar groove (see Fig. 2, D), about 7mm. long, 
2mm. wide, and 2 mm. from the posterior end, whilst at some 3 mm. 
above this there is a shallower and much less regular groove of about 
the same length. Again, on the left side (see Fig. 2, C) and near 
the dorsal area, the surface extending upwards from almost close to 
the posterior fractured end for a distance of about 11 mm., and over 
a width of about 10mm., bears a number of short, irregular, finely- 
incised lines. 
As already stated, the fossil is imperfect at each end; the fracture 
at the alveolar end is comparatively recent, and was probably produced 
during, or possibly subsequent to, the extraction of the specimen from 
the rock. The fracture at the posterior end seems, however, to have 
been produced before the specimen was imbedded in the chalk, and 
most probably at the death of the animal. The marks near the 
posterior end that have been alluded to above seem to have been 
caused by the teeth of some animal, an enemy of the Belemnite, the 
saw-like cuts being produced by two adjacent teeth, and the sharply- 
incised lines by the point of the tooth placed in opposition to these 
two, for it is to be observed that the sharply-incised lines are as 
nearly as possible opposite the space between the two series of jagged 
