PALEONTOLOGY 



303 



a 



the basin of the Great Salt Lake, the same species of fishes 

 and insects were found in all its tributaries. Now that these 

 streams flow separately into a lifeless lake, the same species 

 of fishes occur in them for the most part without alteration. 

 One species of sucker (Catostomus ardens) and one chub (Leucis- 

 cus lineatus) are found unaltered throughout this region and 

 in the Upper Snake River (above Shoshone Falls), into which 

 Lake Bonneville was once drained. Other species are left 

 locally isolated, but one species 

 only (Agosia adobe), a small 

 minnow of the clay bottoms, 

 can be shown to have under- 

 gone any alteration. But with 

 the tiger beetles (Cicindelce) 

 a large number of species 

 have been produced by sepa- 

 ration. 



From the Bay of Panama 

 374 species of fishes are re- 

 corded in the recent mono- 

 graph of Gilbert and Starks. 

 Of these species, 204 are re- 

 corded also from the Gulf of 

 California, while perhaps fifty 

 others are represented in the 

 more northern bay by closely 

 related forms. Comparing the 

 fish faunas separated by the 

 isthmus, we find the closest 

 relation possible so far as 

 families and genera are con- 

 cerned. In this respect the resemblance is far closer than 

 that between Panama and Chile, or Panama and Tahiti, or 

 Panama and southern California. On the Atlantic side, simi- 

 lar conditions obtain, although the number of genera and 

 species is far greater (about 1,200 species) in the West Indies 

 than at Panama. This fact accords with the much larger ex- 

 tent of the West Indies, its varied groups of islands isolated 

 by deep channels, and its near connection to the faunas of 

 Brazil and the United States. 



But it is also noteworthy that while the families of fishes 



FIG. 179. Diagrams showing the series 

 of changes in geological time from a 

 horse's foot of four separate toes (/) to 

 one of one toe and a pair of splint 

 bones (a) ; a-f represent the feet of dif- 

 ferent horselike animals from modern 

 time backward. 



