1896.] NATURAL SCIENCES OF PHILADELPHIA. 425' 



There is no reason why such exceptional forms should maintain 

 themselves, unless there is a niche in the environment which they 

 are especially qualified to fill. 



The small Zonitidce, commonly known as Hyalinia, Conulus, etc., ■ 

 are especially fitted by their size and lightness to be transported by 

 winds, adhering to dead leaves or other light objects. They are also 

 well-adapted to maintain themselves under adverse circumstances, 

 excepting against extreme aridity. Consequently it is not surpris- 

 ing that they, and the small Pupidce of which the same is true, 

 should be found as members of nearly all insular faunas where many 

 other common types are wanting. 



Other small, thin and light shells like Leptinaria, Balea, Suhu- 

 lina, etc., are so easily transported that their presence in insular 

 faunas excites no surprise, though the mystery as to how any of 

 these shells reached their ])reseut habitat remains as provoking as 

 ever. The distribution of laud shells is full of such mysteries, to- 

 ward the solution of which so little has been done. Thus, the Helix 

 (Tachea) suhglobosa of Binney is apparently not distinguishable 

 from the pale unicolorate variety of the H. hortensis of Europe and 

 has been confidently asserted to have been introduced by commerce. 

 It is the only representative of its particular group in America, and 

 is known only from the extreme northeastern border of the United 

 States from Massachusetts to Cape Breton Island, living everywhere 

 close to the sea or even on small islands off the coast. The suspi- 

 cion that this species is an importation is very natural, but never- 

 theless it is found in the clays of the Champlain epoch of the coast 

 of Maine and in prehistoric shell-heaps of the same region, so that, 

 if it was imported, Leif Ericsen had a predecessor in the glacial 

 epoch. The banded forms of hortensis, since imported, do well and 

 multiply varieties without difficulty and in profusion. How did it 

 happen, then, that the importer of the subglobosa brought only one 

 of the rarer varieties and planted it along a thousand miles of 

 coast ? And why should it appear living chiefly on rocky islets, 

 never occupied or tilled by man ? The answer to such questions in- 

 volves matters of the greatest interest and importance in the history 

 of the distribution of life on the globe. Ap^^lied to the Galapagos 

 Islands, it is evident that occupation, especially by sheep, will ren- 

 der it impossible forever to get any complete data. May it not be 

 hoped, therefore, that some one will undertake to make a thorough 

 and complete survey of the malacology of these islands before it is 



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