142 THE CHAIN OF LIFE. 



once find ourselves in the midst of air-breathers of various 

 types. Here are Myriapods, insects of several orders, Spiders, 

 Scorpions, Land-snails, and Batrachian reptiles, and these of 

 many species, and found in many localities widely separated. 

 We can thus people those dark, luxuriant forests, to which we 

 owe our most valuable beds of coal, with many forms of life; and 

 as most of these belong to tribes likely to multiply abundantly 

 where food was plentiful, we can imagine multitudes of Snails 

 and Millepedes feeding on succulent or decaying vegetable 

 matter, swarms of insects flitting through the air in the sunnier 

 spots, while their larvae luxuriated in decaying masses of leaves 

 or wood, or peopled the pools and streams. In like manner, 

 in imagination we can render these old woods vocal with the 

 trill of crickets and with the piping or booming of smaller and 

 larger Batrachians. Let us now, in accordance with our plan, 

 inquire as to the nature of these early air-breathers and the 

 fortunes of their families in the geological history. 



The Land-snails known as yet in the Carboniferous are 

 limited to four species, belonging to as many genera, all 

 American and related to existing American forms. The two 

 earliest known are represented in Figs. 124 and 125.^ One of 

 them is a Pupa, or elongated Land-snail, so similar to modern 

 forms that it does not merit a generic distinction, and is indeed 

 very near to some existing West Indian species. The other is 

 in like manner a member of the modern genus Zonites. These 

 are from the Coal-formation of Nova Scotia, and the Pupa must 

 have been very abundant, as it has been found in considerable 

 numbers in a layer of shale, and in the stumps of erect trees, 

 in beds separated from each other by a thickness of 2,000 feet 

 of strata. The Zonites is much more rare. The other two 

 species occur in the Coal-field of Illinois, and have been de- 

 scribed by Bradley. One of these is a Pupa still smaller than 

 P. vetusta, and, like some modern species, with a tooth-like 



^ The enlarged figure of Pttpa vetusta is too much elongated, and the 

 aperture is somewhat conjectural, as it is usually crushed. 



