428 
Channel, may have been transported thither during one of the tem- 
perature minima of Europe. On the sea-bottom along the British 
Islands, and im the Biscaya, many northern shells, now extinct 
there, are deposited, eé. g. Portlandia arctica, Leda pernula, AÅrca 
glacialis, Pecten islandicus, Astarte borealis, Tellina calcarea, Mya 
truncata var. uddevallensis. One of these forms, Portlandia arctica, 
lives at the present time only in tracts where the winter tempera- 
ture is below 0? C. The fact that such a species is secured in 
the dredge together with recent specimens shows that the bottom 
deposit in many places has been formed very slowly. If a shell 
is more than a few years old, we can not from its appearance 
conclude anything with regard to its age. We can not decide 
whether it be 100 or 100000 years old, whether it be post-, inter- 
or préglacial. That many southern species are found. among the 
shallow-water shells at great depths prove nothing to the effect, 
that these forms can not have been transported by the floating ice, 
as they may belong to a previous temperature maximum (an inter 
or préglacial period). 
In transporting sea- weeds, on which molluscs are fixed, the 
surface currents can also contribute to carry the shells out at depths 
not their natural area. On this way of shell-spreading R. Vallen- 
tin has made some observations, and an extract of his report about 
this will be quoted here") (p. 4£20—21): I ,,have been fortunate 
enough to secure two specimens of bivalve molluscs while being 
dispersed by floating seeweed; and, strange as it may appear, one 
was a specimen of Cardium edule, a long frond of Chorda filum 
being attached to the left valve by its base. This molluse was 
secured a mile from land, and was found on examination to be 
alive and in a healthy condition.... A short time later a fine living 
example of Mytilus edulis was secured under similar circumstances 
and weighed 23,3 grm..... Numerous examples of single valves of 
1) R. Vallentin: ,Some Remarks on the Dispersal of Marine Animals 
by means of Seaweeds". Ann. & Mag. Nat. Hist. VI. Ser. Vol. 16. 
1895. 
