898 NEW YORK STATE MUSEUM 



The effect on the organisms is of two kinds, first the dwarfing, 

 and second the modification in form. The amount of dwarfing 

 varies in each group, apparently according to the habits of the 

 group. Iron in solution in water tends to settle gradually to 

 the bottom, as was found in experimenting on the fishes, etc. in 

 the aquariums. Thus the bottom layers of water are denser and 

 more impure. The forms living wholly on the bottom are thus 

 most affected. Therefore it is not surprising to find that the 

 brachiopods, which are either sessile or lie on the bottom, are 

 the most dwarfed. There is also great uniformity in the size of 

 the individuals of a given species, due to their spending their 

 whole life in the iron water. No single brachiopod has been 

 found which was larger than the natural adult size for pyrite 

 forms of that species. All the exceptions to the universal 

 dwarfing occur in the other groups. The only period when the 

 brachiopod is free swimming is during larval life; and, with the 

 dwarfing beginning then and continuing all along, by the time 

 the protegulum is formed, the animal is strikingly a pygmy. 

 The adult brachiopods in the pyrite are seldom one fifteenth 

 the diameter of the ancestral form. Lamellibranchs are also 

 greatly modified, and show uniformity in size. One genus, 

 Paracyclas, is uniformly one twenty-fifth the diameter normal 

 to the species, and no larger individual has been observed. 

 However, most of the lamellibranchs are only one fifth to one 

 third the normal dimensions, and have thus for some unknown 

 reason resisted the unfavorable environment better than the 

 other groups. Their larvae are free swimming, and the adult 

 moves about in a limited way, but they seem to have been 

 brought up in the iron water. There are however no unusually 

 large individuals or any which really approximate the size of 

 normal adults in the Hamilton fauna. The lamellibranchs as a 

 group are in a phylembryonic stage of development. It seems 

 to be true in general that primitive members of a group have 

 greater vitality in resisting unfavorable circumstances, and it 

 may be that these forms are to be considered as primitive or 

 ancestral. The gastropods and cephalopods possess, during 

 their whole life, greater locomotive ability. Here there is a 

 great variation in the size of the individuals of each species. 

 Sometimes a form is one twenty-fifth the diameter of the ances- 



