CAPE SABLE 81 



is covered with sharp, siliceous spicules, first one 

 way and then the other, and so laboriously drills 

 out the material in which it lives. It is here I 

 found a couple of specimens of the exceedingly rare 

 Cancellaria tenera, the shell having flat, tabulated 

 shoulders like a miniature stairway, but it is not 

 especially beautiful. 



Although nearly all the vegetation and most 

 of the dry-land animal life of this region are 

 tropical, derived in all probability, as I have else- 

 where shown, from the Upper Keys over an old 

 but now destroyed landway, the marine forms, on 

 the contrary, are largely warm temperate or at 

 most subtropical. This may at first seem strange 

 but the explanation is simple. The tropical 

 marine life of the keys has been brought to them 

 by the Gulf Stream. But these very same keys 

 and the plateau on which they rest, act as a barrier 

 to the farther passage of this life to the Florida 

 west coast. The water on the west coast of 

 Florida is shallow for miles out from the shore and 

 the Gulf Stream flows far to the westward. This 

 wide belt of shallow sea often becomes quite cold 

 in winter, especially in time of severe northers, 

 and is therefore decidedly unfavorable for strictly 



