482 



THE AMERICAN NATURALIST [Vol. XLII 



species, few of which, though adults, are over 2 mm. in 

 diameter. The fauna includes 1 Mastoid, 15 braehiopods, 

 12 pelecypods, 6 gastropods, 2 pteropods, 7 cephalopods, 

 1 trilobite, and 2 ostracods. These have all, however, 

 been dwarfed until their average size is only one fifteenth 

 that of the same species in the preceding Hamilton. The 

 cause of this dwarfing is suggested to be the presence of 

 much iron in solution and the gases arising from the 

 decaying vegetable and animal matter. 1 ' The iron in the 

 water, as ferrous carbonate, was probably precipitated by 

 the sulfuretted hydrogen" from the organic matter, and 

 thus formed pyrite (FeOC0 2 + H 2 S = FeS + C0 2 + 

 H 2 0). 24 



That iron in the water has a dwarfing effect was shown 

 by experiments upon fishes and tadpoles 25 which in eight 

 months had been retarded in growth from three to five 

 mm. The same is apparently shown in the fauna of the 

 oolitic iron ore of the Clinton beds; in these beds at 

 Rochester, N. Y., the species have "an average of about 

 one third the diameter of the same species in the beds 

 just above and below." 20 



The same condition was noticed in similar beds in Ken- 

 tucky. 



The following list will give a general view of the aver- 

 age size of the dwarfed forms. Loomis gives the average 

 measurement of each species. 



Spirifer fimbriatus mut. pygmaus Loomis is shown to 

 be one twenty-fifth the normal size of the species. 



Nucleospira concinna mut. pygmcea Loomis is one 

 fifteenth that of the species. 



Tropidoleptiis carina f us mut. pygmceus Loomis is one 

 fifteenth. 



Nucula hrata unit, pygmcea Loomis averages one tenth 

 the size of the normal species. 



Paracyclas hrata mut. pygmcea Loomis is only one 

 twentieth. 



21 Loc. ext., p. 920. 



