5 oa PREHISTORIC E UROPE. 



number of northern species, such as Necera rostrcda, Spr. ; Verti- 

 cordia abyssicola, Jeff.; Dentalium dbyssorum, Sars; Buccinum 

 humphreysianum, Bennet; and Pleurotoma carinatum, Bivona, 

 commingled with which were Mediterranean forms, which im- 

 parted somewhat of a southern character to the assemblage. 

 Among these were Ostrea cochlear, Poli; Aporrha'ls serresianus, 

 Mich. ; Murcx lamellosus, Cristof. and Jan. ; and Troclms granu- 

 latus, Born. 1 Similar noteworthy " finds " have been recorded 

 by Gwyn Jeffreys and others off the coasts of the Shetlands 

 and the Outer Hebrides, and Morch mentions that several genera 

 of molluscs, which indicate a southern climate, are still found 

 on the west coast of Iceland, such as Actccon, Trochus, Patina, 

 Nassa, Mactra (elliplica), none of which is arctic. When we 

 cross the Atlantic to the Gulf of St. Lawrence we encounter the 

 same remarkable phenomenon. Professor Verrill has shown that 

 there are genuine colonies of southern species in that gulf and 

 on the coast of Nova Scotia, which are completely isolated from 

 their co-species of the southern coast of New England, and 

 surrounded on all sides by more northern forms. 2 And he tells 

 us further, that at an earlier period these colonies were much 

 more extensive. The shells of the round clam or " quahog " 

 (Venus mercenaria) are abundant in the mud in places where 

 no living ones could be found, and they likewise occur in great 

 quantities in certain old Indian shell-heaps on many of the 

 islands in Casco Bay, upon the coasts of which they do not now 

 live. " That at a more remote period," says Verrill, " the marine 

 climate of this region was still warmer, and the southern species 

 were more abundant than during the period when the Indian 

 shell-heaps were formed, is shown by the occurrence of great 

 beds of oyster- shells a few feet beneath the mud in Portland 

 harbour, where they are associated with quahogs and several 

 other southern species, among which are Callista convexa, Tur- 

 bonilla interrupta, and Pecten irradians. The last is not known 

 to live at present north of Cape Ann, on the New England 



1 The Depths of the Sea, p. 86. 

 2 Amer. Joum. of Science and Art, Third Series, vol. vii. p. 134. 



