34 



THE AMERICAN NATURALIST [Vol. LIII 



rather loose and friable, consisting principally of *'Ti- 

 jeras fine sandy loam" and containing, near the surface, 

 a relatively large proportion of fine angular gravel and 

 wind-blown sand. The color is a yellowish or yellowish 

 brown. The vegetation is sparse, consisting of scattered 

 grasses, Chrysothamnus, Gutierrezia, Salsola, Yucca, etc. 

 This species is not found in the adjoining valley of the 

 Eio Grande, nor in the mountains (Sandias) which border 

 the *'mesa" on the east (2,200 meters and above), where 

 moister conditions prevail. In the mountains the i^in- 

 fall is probably twice as great, on the average, as on the 

 *'mesa," although accurate data are not available, and the 

 evaporation is much less, due to the lower temperatures 

 which prevail. In the valley the water table is very near 

 the surface of the soil (actual soil surface or above to 

 5 meters below the surface) . Standing water is not found 

 on the clinoplane except after very heavy rains, which 

 sometimes fail for months. 



Phrynosowia douglassii ornatissimum, specimens of 

 which were obtained with the above, has a much less re- 

 stricted habitat, both locally and regionally. It is dis- 

 tributed over a great deal of the eastern slope of the 

 Eocky Mountains, even as far north as Canada, and, 

 locally, extends into both of the regions described above 

 as bordering on the clinoplane. It is, indeed, more abun- 

 dant in either of these than in the clinoplane region be- 

 tween, indicating that the determining factor in the dis- 

 tribution in this case is similar in the lower valley and 

 on the mountain side. As mentioned above, the aridity 

 of these two regions is much less than that of the clino- 

 plane. The soil differences are also marked, in that the 

 moister soils are more dense and contain more humus, 

 derived from the more abundant vegetation. However, 

 the variation in both regions is very great, from heavy 

 clay to fine sand in the valley and from native rock to fine 

 sand in the mountain. 



Phrynosoma cormitum does not occur in the same local 

 area as that occupied by the species previously mentioned. 



