DWARF FAUNAS AND MICROFAUNAS 1067 



As an illustration of the dwarfing due to the freshening of sea 

 water Shimer cites the organisms of the Black and Caspian Seas, 

 which are freshened by the influx of stream water (see tables of 

 salinity, pp. 146, 154). As shown by Forbes (14), the species of 

 molluscs in the Black Sea are all smaller than those same species 

 in the British seas. Cardium ediile. the common cockle of the 

 British coast, is dwarfed when it lives in the brackish water of 

 the estuaries. The shell is not only reduced in size, but becomes 

 thin and has its external character less strongly marked. The 

 cockles of the Caspian Sea are small, thin, and smooth, with lateral 

 or central teeth or both suppressed. The cockle of the Green- 

 land estuaries is likewise thin, smooth and almost edentulous, the 

 rudiments of hinge-teeth occurring in the young but disappearing 

 in the adult. This species is abundant in the Pliocenic Crag de- 

 posits of Suffolk and Norfolk, especially in the fluvio-marine por- 

 tion. Among other species dwarfed by brackish water are Mva 

 arenaria and Littorina lit tor ea. 



Shimer described a diminutive Pleistocenic ? fauna from the 

 estuarine clays of the Hudson bottom opposite Storm King, 40 

 feet below the bed of the river. This fauna consisted mainly of 

 large numbers of Mulinia lateralis fSay) and a lower development 

 of Trivia triviftata Say. These species live at present oflf the New 

 England and New Jersey coasts in normal marine or but slightly 

 freshened water, where their size is almost twice that of the Hud- 

 son estuary specimens. 



Dwarfing due to concentration of salt, i. c, increase in salinity, 

 is shown to some extent in the Mediterranean, which, with a salinity 

 of 39 permille, has many of its species smaller than their repre- 

 sentatives in the open water of the British and Spanish coasts. 

 The dwarfed faunas of the European Permic have in part been 

 ascribed to such concentration of the water. The possibility of 

 dwarfing of faunas through an excess of iron salts has been shown 

 by experiments upon fishes and tadpoles, which in eight months 

 were retarded in growth from 3 to 5 mm. Fossil examples are 

 found in the Pyrite layer, which in the Genesee \'alley and west- 

 ward in New York replaces the Tully limestone of the Upper 

 Devonic. In this the fauna of 45 species was found by Loomis 

 (28) to be on the average only one-fifteenth the size of the normal 

 form. The dwarfing was apparently due to presence of much iron 

 in solution, in the form of ferrous carbonate, and this was precipi- 

 tated as pyrite by sulphuretted hydrogen derived from the decay- 

 ing organic matter (FeOCO,+H,S=FeS+CO,-|-H,0). The 



