Cambridge Philosophical Society. 215 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 

 [Continued fi'om vol. xii. p. 403.] 



March 10, 1856. — A paper was read by L. Barrett, Esq., " On the 

 Distribution of the Mollusca on the Coast of Norway." {Vide Annals 

 of Nat. Hist. May 1856.) 



In this the author observed, that when the fauna of the coast of Nor- 

 way is compared with that of the other side of the North Atlantic, a 

 great difference will at once be perceived, not only in the number of 

 species, but also in the different distribution of northern and south- 

 ern types ; the Mollusca of Greenland being peculiarly arctic, those 

 of Scandinavia a mixture of southern and northern species. In the 

 southern part of Norway we find the species living on our coasts 

 abundant ; but they become rarer as we go north, their place being 

 supplied by arctic forms. Many of the northern species have a great 

 geographical range, at which we need not be surprised when we 

 consider their great antiquity, many of them having existed since the 

 pliocene period ; and, in the author's opinion, whenever we find a 

 species with a great geographical range, we may at once infer that 

 it has continued to live from a remote period. It is extremely diffi- 

 cult, according to the present state of the currents in the northern 

 seas, to account for the wide distribution of arctic shells on this side 

 of the North Atlantic ; but when we consider that at not a very 

 distant period the temperature and other conditions of this area 

 were totally different, that a cold climate prevailed, certainly accom- 

 panied by a current setting from the north (as is fully proved by the 

 fact that boulders are always found nearly south of the moun- 

 tain ranges from which they have been originally transported), and 

 that many of the shells are found fossil in the Sicilian tertiaries, 

 this wide distribution may be fully accounted for. As these frigid 

 conditions were gradually altering to more genial ones, those species 

 requiring a lower temperature would gradually die out, and only con- 

 tinue to exist in higher latitudes. The littoral and shallow water 

 species would be most affected by such an alteration of climate ; 

 and while the fauna of the littoral and laminarian zones ■would be 

 entirely changed, — the shells composing that fauna replaced by other 

 species, — those living in the deep sea would continue to exist, per- 

 haps at a greater depth, mingled with the species brought in with 

 the new physical conditions of the area. This we know to be the 

 case ; for while the northern littoral shells, such as My a truncata, 

 &c., are found only fossil in Sicily, many of the deep-sea arctic species 

 that existed there when those fossils were alive are still found living 

 in the deeper parts of the Mediterranean. 



The same thing occurs on our coasts, where the arctic littoral 

 or shallow-water shells, as Astarte arctica, Tellina proximo, Natica 

 helicoides, &c., which are found in shallow water on the Scandi- 

 navian or Greenland coasts, are now rare as deep-sea shells, and that 

 in the same area in which they were formerly abundant as shallow- 

 water epecies. Some species are capable of enduring great differences 



