24 



Aud six other species of mollusks which he enumerates 1 He then says, "It 

 is remarkable that the specimens of the first seven species are well developed, 

 and decidedly larger than any now found in the neighborhood. This is espe- 

 cially the case with the C'ardlum eclule, aud Litorina litorca, while the oyster lias 

 entirely disappeared, and, even in the Kattegat, occurs only in a few places ; a 

 result which may, perhaps, be partly owing to the quantities caught by fisher- 

 men." "And lie concludes that "on the whole their disappearance, especially 

 when taten in connection with the dwarfed size of other species, is evidently 

 attributable in a great measure to the smaller proportion of salt in the water." 



Among the birds occuring in the Danish shell heaps, is Tetrao urogattm, 

 which feeds principally on the buds of the pine, showing that at the time the 

 deposits were made, extensive pine forests once covered the region, a fact pre- 

 viously established by a study of the peat beds. Bones of the great aulr, Alca 

 impennis, also occur in the same deposits, and this bird is now probably extinct. 



The shell mounds along the coast of Maine also indicate a marked change in 

 the distribution of certain species. A number of species of mollusks occur in 

 them, Avhich are not found at present north of. Cape Cod. Some of them pre- 

 sent a remarkable solidity of form in comparison with recent specimens. 



The bones of the great auk are likewise met with in many of the deposits, in 

 such numbers as to show that it was then, a common bird, and furnished an ar- 

 ticle of food. More curious still is the occurence of a molar tooth discovered by 

 nie in one of the deposits on the coast of Maine, which Prof. 'Wyman beieved 

 to be the molar tooth of the polar bear, a species which is now confined to the 

 .Arctic regions. 



In a paper published fifteen years ago on the occurrence- of land snails iu an- 

 cient deposits on one of the islands in Casco Bay, Maine,* I showed that at the 

 time of their existence, a hard wood growth must have abounded. The island 

 has been covered since the earliest memory of mail with a dense spruce growth. 



I have iu preparation a paper on the changes in the character of certain spe- 

 cies of Mollusca from the deposits in Massachusetts. In those I have measured 

 and drawn, the differences between present existing species and their ancestors 

 are constant. 



Prof. "Wyman observed similar changes in the mollusks of the Florida de- 

 posits. He says, in his memoir on the Florida Mounds, that the Ampullaria?, 

 and Paludime, are much larger than their living representatives. " The average 

 size of the aperture in twenty large Ampullaria? from the mounds was, breadth 

 31.4 mm, and length 53.9 mm ; while in the largest living shells we have 

 found, the aperture did not exceed 30 mm. in breadth and 48 mm. in length, 

 which would seem to indicate a greater vital activity in fornier days." 



* On the occurence of rare Helices in ancient shell heaps. Proceedings Portland Soe. Nat. Hist. 

 Vol. 1 1863. 



