MOLLUSCA. 
(Exclusive of Cephalopoda.) 
By Charles Hedley. 
(Plates I.-IX.) 
Our knowledge of the south polar Mollusca has been considerably enlarged during 
the past 20 years by the work of various Antarctic Expeditions. These gains are 
represented by a sketch of the literature compiled by Messrs. Melvill and Standen,* 
and by catalogues arranged by Drs. H. Strebel,*j" P. Dautzenberg, H. Fischer,J and 
J. Thiele. § 
Though few observations have been made, it is apparent that Antarctic waters 
differ from those of temperate seas by greater uniformity in vertical section. Penetration 
of light in these high latitudes must be brief owing both to the angle of incidence from 
a low sun and to the dense screen of a richer plankton. Where the temperature of the 
surface scarcely rises above freezing, the whole column of several hundred fathoms 
from the waves to the ground can hardly vary a degree. 
Consequently, barriers that elsewhere confine the sublittoral fauna do not exist 
here ; and such fauna, except for absence of algse, can range from beach to abyss through 
an almost identical environment. 
Probably change from stones to ooze is the chief factor to affect distribution, and 
much of the deep area usually spread with ooze must be paved with moraine matter 
spilt from capsized icebergs. 
The intense cold maintains a similar climate throughout the whole Antarctic 
periphery, while vigorous westerly winds establish rapid communications of drifting 
spores and larvae between one district and those that lie to leeward. Monotony of 
environment thus tends to produce a uniform fauna and flora. A striking circumpolar 
distribution is shown by the largest and most conspicuous shells such as Neohuccinum 
eatoni, Chlamys colbecki, and Laternula elliptica. As the less conspicuous species are 
examined they will agree with the more prominent forms. 
* Melvill and Standen.—Scientific results of the Scotia Expedition, v., 1907, pp. 124-127 and vi., 1912, pp. 138-140. 
t Strebel.—Schwed. Siidpol. Exped. vi., 1908, pp. 86-93. 
} Dautzenberg and Fisclier.—Result Camp. Seient. Monaco, xxxvii., 1912, pp. 10-15. 
§ Thiele.—Deutsch. Siidpol. Exped. xiii., 1912, pp. 257-270. 
Dr. G. Pfefier considered that circumpolarity in the marine fauna is more developed in the Arctic than in Antarctic 
regions (Ann. Mag. Nat. Hist., April, 1901, p. 302). Available information seems to me yet insufficient for this comparison. 
