No. 499] 



DWARF FAUNAS 



479 



(These measurements were taken from the figures.) 



(b) Great Depths. — The pauperization of faunas with 

 increase in depth appears to be due primarily to the 

 decrease in light, which is essential to plant growth, and 

 thus indirectly to animal life. Secondarily it is due to the 

 decrease in temperature, the increase in the heavier con- 

 tents of the water, and the greater pressure with depth. 



In Geneva Lake the deep fauna is small and sluggish 

 while their surface representatives are larger and active. 



In abyssal ocean faunas there are few mollusca, and 

 these are small, translucent, and white, with few crabs 

 and annelids, but many echinoderms and porifera. 19 



With decrease in size from higher to deeper regions 

 there is further pauperization, evidenced in the loss of 

 brilliant coloring and variety of pattern. In the Mediter- 

 ranean the proportion of colored to uncolored shells at 

 depths of 35 to 55 fathoms is 1 to 3 ; at 100 fathoms and 

 over, it is 1 to 18. 20 



The very many dwarf or depauperate fossil faunas 

 already noted in the literature are doubtless but a small 

 fraction of those still unnoted. The causes which are 

 active at present in effecting this result were very prob- 

 ably equally active during each year of each era some- 

 where upon the earth's surface; so that the total number 

 of such examples must be very great. Some of the fossil 

 faunas, as for example, that of the Genesee, consist of uni- 

 formly small species, a selective agency having discarded 

 the larger ones; here no stunting of growth is apparent. 

 In such other faunas as that of the Pyrite bed of the 

 Tnlly horizon, all of the individuals are smaller than the 

 normal individuals of those species, thus showing very 

 decidedly the stunting effect of environment. In still 

 ether cases, such as the Tertiary deposits at Steinheim, 



the' environment, becoming dwarfed in size or of a bizarre 

 shape, while the rest of the fauna were of the normal 

 size for the species. 



