1 2 Proceedings of the 



fered from the severe cold. He found at two several places, about half- 

 way between Leith and Portobello, great numbers of the common swim- 

 mer crab (Portunus depurator) lying dead ; the common shore-crab, too 

 (Carcinus mcenas), seems, judging from the number recently killed, also 

 to have suffered ; and in the perished Mactra he detected several speci- 

 mens of that minute Pea-crab (Pinnotheres pisum) , which finds shelter 

 within the living shells, and which seem to have shared in the fate of 

 their involuntary hosts. Among the dead crustaceans he found a newly 

 tilled specimen of the rather rare masked crab (Corystes cassivelaunus), 

 a female laden with spawn. 



He deemed it worthy of remark, that there are shells very abundant 

 on the coast, and which, from their littoral character, must have been 

 quite as much exposed to the intense cold as either Mactra stultorum or 

 Solen siliqua, of which he did not find a single dead specimen on the 

 beach. Tellina solidula is one of these species, and M actra solida, with 

 its sub-species or variety Mactra truncata, another ; and these the frost 

 seems not to have in the least affected. Of the various littoral univalves, 

 too, including the periwinkles, purpura, and trochidse, only one species, 

 Natica inonilifera, seems to have suffered. Now, Tellina solidula is 

 in some localities, as at Castleton King-Edward, one of the most nume- 

 rous and best developed of the boreal shells ; Mactra solida is also a 

 boreal species, with the common periwinkle Littorina littorea), the com- 

 mon purpura (P. lapillus), and the dog-periwinkle (Trochus cinera- 

 rias). Again, on the other hand, of the destroyed shells, he had not yet 

 found any trace of Tellina fabula or Donax anatinus in the old glacial 

 deposits, such as the boulder clay or Gamrie gravels and sands, nor yet 

 of Mactra stultorum or Solen siliqua, though the former is said to be a 

 shell of the Mammiferous Crag, and the latter of the Clyde bed&. And 

 though a large natica occurs in both the Caithness and Gamrie deposits, 

 that very considerably resembles Natica inonilifera, it fails to exhibit 

 the characteristic flexuous streaks, and, in general form, seems at least as 

 much akin to a sub -arctic species as to the one recently killed by the frost. 

 And there could be, he thought, no doubt that the boulder clay Tellina, 

 T. proxima, is altogether a different species, notwithstanding its points 

 of similarity in the more dwarfish individuals from Tellina tenuis. None 

 of the molluscs killed in any considerable abundance by the present in- 

 tense frost seem to be truly boreal species ; and their destruction by the 

 refrigerating agent, which has strewed them by millions along the beach, 

 seems not only strikingly illustrative, as he had said, of one of the modes 

 in which species may be destroyed, but also of a curious passage in the 

 later geologic history of northern Europe. It is an ascertained fact, that 

 shells were living in the British area during the times of the Red Crag, 

 of the same species with those recently killed by the frost ; Mactra stul- 

 torum is one of these, and Natica monilifera another, and they now live 

 in the neighbouring firth ; but he at least had failed, after sedulous ex- 

 ploration, to detect them in the intermediate period of boreal shells, ice- 



