892 = G. C. Crick—Actinocamax from the English Chalk. 
the original of those figures; the compressed form of the alveolar 
end of the present example serves, however, to distingnish it from 
Actinocamax Grossouvrei. The fossil appears to be intermediate 
between Actinocamax Alfridi and Actinocamax Grossouvrei, but it 
does not appear to be identical with any described form of the genus. 
The present writer has therefore great pleasure in naming the species 
after Dr. H. P. Blackmore, F.G.8., of Salisbury. 
Horizon and locality.—Dr. Blackmore’s specimen was obtained from 
the chalk-pit at West Harnham, near Salisbury, at the base of the 
zone of Actinocamax quadratus. It is from a somewhat higher 
horizon than the Gravesend specimen which is described below. 
ACTINOCAMAX sp. 
Description.—The specimen (Fig. 2) consists of about two-thirds of 
the length of the guard, the posterior third being entirely wanting. 
The anterior end is much fractured, especially on the ventral side, 
so that there is no trace of a ventral fissure if such existed, but 
a small piece of the dorsal part of the alveolar border is preserved ; 
this seems to show that originally the alveolar end was only slightly 
excavated; before being imbedded in the chalk mud, however, this 
end was somewhat deeply excavated, but this excavation evidently 
did not form part of the original alveolar end, as is clearly shown by 
the angle at which the side of this cavity meets the small piece of 
the smooth original alveolar surface which is preserved. The sides 
of this cavity are also very irregular and covered with small pyramidal 
masses of a fibrous crystalline material (calcite), so that it is quite clear 
that they did not constitute the sides of the alveolus,! these latter being 
smooth and having precisely the same angle of inclination as the 
sides of the phragmocone. Nor does the cavity appear to have 
been that not infrequently produced in some forms of Actinocamax 
owing to the decay, after the death of the animal, of the uncalcified 
portion of the guard immediately surrounding the phragmocone.’? 
Doubtless the central portion of this end of the guard was very 
imperfectly calcified, and was therefore easily disintegrated after 
the guard became detached from the animal. That the guard was 
exposed to the action of the sea for some time after the death of the 
creature is clear from the numerous sponge-borings by which it is 
traversed. Owing to the fractured condition of the anterior end, 
the dimensions of this part of the guard can best be taken at about 
10 mm. below the alveolar border; here the transverse section of the 
guard is oval, the ventro-dorsal and transverse diameters being 12 
and 10°5 mm. respectively, and the greatest width at a distance of 
about one-third of the ventro-dorsal diameter from the ventral surface. 
1 The term ‘alveolus’ is frequently somewhat loosely applied. The ‘alveolus’ is 
really the conical cavity at the proximal end of the guard of a typical Belemnite into 
which the phragmocone fits. Usually, however, in the genus <Actinocamax the 
portion of the guard immediately in contact with the sides of the phragmocone was 
not calcified, and during fossilisation was destroyed; when, therefore, a conical 
cavity is preserved in the genus its sides are not those of the ‘alveolus,’ but those of 
a cavity having a greater angle than the ‘ alveolus.’ 
* See figures of the alveolar end of various forms of Actinocamax in the GxOL. 
Mae., 1904, p. 409. 
