10 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
Superfamily CRANIACEA Waagen. 
Genus Crania Retzius, 1781. 
Genotype Anomia craniolaris L. 
Crania joubini sp. nov . 
(Plate XVI, figs. 18, 19.) 
Habitat. —Station 9; lat. 65° 20' S„, long. 95° 27' E. (Davis Sea), 240 fathoms, 
24th January, 1914. Sea bottom, small rocks. 
A single specimen of a dorsal valve of a species of Crania was dredged from 
Station 9. The shell was without any trace of the animal, and had evidently been dead 
for some time, as it contained the tube of a calcareous annelid on its inner side. In 
shape it is somewhat irregular, owing to a feeble development of the left posterior corner 
in the latest stages of growth, but the course of the growth lines shows that it has 
developed from a roundly rectangular shape, broader than long. The convexity is 
very slight, and the margins of the valves are not in one plane. The blunt apex is 
situated very close to the posterior border, where the steepest slopes exist. The shell 
also slopes more steeply to the right than to the left side, which is arched about half¬ 
way between the apex and the left anterior corner. Growth lines are not prominent 
except in the outer third of the shell. There is no trace of radial costation or striation. 
A light brown epidermis covers the greater part of the surface, but where this is 
removed, as on the apex and round the anterior margin, the shell is white. 
In the interior there is a narrow, finely-granulated rim, limited by an indistinct 
shoulder. The muscular impressions are not strongly marked, and only the posterior 
and anterior adductors and one of the dorsal protractors can be distinguished under 
favourable conditions of lighting. The pallia! sinuses have left no impressions. The 
fine punctation can be easily distinguished on the interior by the aid of a lens. 
The dimensions of the specimen are—length 7-8 mm., breadth 9-2 mm., height 
2 mm. 
The shape and ornament of this specimen are approached more nearly by 
northern than by southern recent forms. The only species of the genus hitherto 
described from Antarctic waters, Crania lecointei Joubin, possesses a nearly central 
apex and growth lines which develop from rounded through elliptical to roundly ovate. 
These differences in shape and in development seem sufficient to prevent the association 
of the present specimen with that species. 
The other forms from the southern seas, Crania patagonica Dali, from the west 
coast of Patagonia, C. Suessi Reeve, from East Australia, and C. huttoni Thomson, 
from New Zealand, have all a radiating ornament, and are thus clearly distinct. Crania 
joubini differs from C. anomala and other northern forms by its feeble convexity and 
the poor development of the muscular impressions. 
The only known Tertiary fossil form of the genus from the Southern Hemisphere 
is the Australian Crania quadrangularis Tate, which is similar in form to the present 
species, but has fine radial striae and strong muscular impressions. 
