SOME SOURCES OF OUR FAUNA AND FLORA 303 



have reached Michigan while Lake Chicago and its successors 

 drained by way of the Illinois and the Wabash, since now all 

 the streams of Michigan are part of the St. Lawrence drainage 

 system. That some of the more hardy of the clams did follow 

 the glacial retreat closely is evidenced by the fact that their 

 shells are found in undisturbed beaches of the post-glacial lakes. 



Of the 150 species of fresh -water fishes found in Illinois that 

 are native to the state " there are 58 species of the east Gulf and 

 Florida district" (Forbes and Richardson, The Fishes of Illinois, 

 " Natural History Survey of Illinois "). From the west Gulf and 

 Rio Grande region there are forty-seven species of fish (same 

 authority).' From this same southwestern center come such 

 animals as our pocket gopher, rattlesnake, six-lined lizard; and 

 such plants as the dune cactus, Andropogon scoparius, A.fur- 

 catus, Panicum praecocius, Schedonnardus paniculatus, Cyperus 

 aristatus, C. acuminatus, Eleocharis tenuis, Carex tribuloides, 

 Asclepias tuberosa, Silphium terebinthinaceum, Rudbeckia hirta, 

 all plants that find congenial habitat in the dry sandy areas or 

 the dry prairies. 



From the Atlantic coastal plain region our fauna and flora 

 have received many contributions. It will be recalled that 

 during the retreat of the glacier our Great Lakes region was in 

 much more direct communication with the Atlantic seaboard 

 than it is at present (Fig. 52). There are fifty- three of the fish 

 of Illinois that have come from Quebec and the New England 

 region. As already noted, some of our clams come from this 

 eastern center, possibly originally emanating from the south- 

 eastern center, but if so migrating to our region by way of the 

 coastal plain. A large number of the plants found along the 

 shores of the Great Lakes seem to have come from this source. 

 A few may be mentioned, such as Panicum verrucosum, P. oligo- 

 santhes, Aristida tuber culosa, Ammopkila arenaria (marram 

 grass), Eleocharis melanocarpa, Psilocarya scirpoides, Fuirena 

 squarrosa, Cakile edentulata (sea rocket), Euphorbia polygonifolia 

 (seaside spurge), Xanthium echinatum (cocklebur). 



