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THE AMERICAN NATURALIST [Vol. XLII 



2. Influence of Mud and oilier Mechanical Impurities in 

 the Water.— Though the western Mediterranean contains 

 a dwarf fauna, yet it is the eastern part which is especially 

 so characterized. This is attributed by de Lapparent 8 

 to the presence in the water of the eastern basin of many 

 very fine particles of solid matter (Nile sediment) which 

 becomes deposited only very slowly. A similar cause ap- 

 parently aided in dwarfing some of the faunas of the 

 Windsor (Nova Scotia) Carboniferous, also those of the 

 Cobleskill, Kondout, Manlius, Bertie, etc. 



3. Influence of a Floating Habitat. — Form* which live 

 attached to floating seaweed will tend to be small owing 

 to the fact that the increased weight of the individual due 

 to growth will cause its sinking with its attached seaweed 

 before the attainment of large size. Hence only the 

 smaller individuals would occur on the seaweed or in the 

 sediment beneath. Fuchs has shown 9 that in the eastern, 

 shallower part of the harbor of Messina, the sea is now 

 filled with different kinds of alga?, densely crowded 

 together. This seaweed thicket swarms with small niol- 

 lusks, seeking here food and protection. Here are species 

 of Rissoa, Trochus, Turbonella, Columbella, Marginella, 

 Cerithium, Cardium, Cardita, Lucina, Area and Venus, 

 but they are throughout of smaller size than normal. 

 This dwarf fauna is thus not the result of stunted growth 

 but is very probably due to the fact that the alga? can not 

 support large and heavy shells. Such dwarfing and also 

 thinning of shells fastened to seaweed (giant kelp) 

 Arnold 10 notes in the case of Pecten latiauritus var. 

 fucicolus of the California coast. This in its floating 

 habitat far from shore is not subjected to the shock of 

 the breakers, and hence the shell not only remains thin 

 but also gradually loses its ribbed ornamentation. P. 



