Gregg — Pheidole rhea 
71 
the above series. Dates on which the ants were obtained 
are March 2 , 1947 (wingless female), June 18, 1947; 
March 29, April 10, April 14, and April 25, 1948. Besides 
these specimens, a few soldiers and numerous workers 
have been added to our collection from Colossal Cave 
State Park, southeast of Tucson, Arizona, which we 
visited on April 20, 1948. The ants were collected as 
they foraged for the. seeds of various desert plants near 
the entrance to the cave. , 
On comparing my material with the detailed descrip- 
tions published by Smith for the soldier and worker of 
rhea , it seemed that a new form of the species might be 
recognized, especially in view of the much greater size of 
the soldiers in my samples and certain differences in 
the queen. However, after studying specimens from the 
Pinal Mountains and the Santa Catalina Mountains of 
Arizona (sent respectively through the courtesy of the 
United States National Museum and the Museum of 
Comparative Zoology), the variability of the species 
noted by Smith is fully confirmed, and it is impossible to 
discern adequate bases for erecting a new subspecies at 
this time. Nevertheless, it is desirable to record certain 
features of my Nogales specimens which depart from 
the published accounts. 
The great variability and continuous gradation in size 
from the smallest to the largest individuals makes it 
difficult to distinguish rhea from other species if only the 
smaller intermediates are available, although its long 
epinotal spines should suffice. The upper size limit of 
the soldier has been uncertain, and Smith gives 5.5 mm. 
as the size for the soldier in his description. He does 
mention, though, an unusual soldier from Escuinapa, 
Mexico, which is 8 mm. The soldiers which I have mea- 
sured reach 9.8 to 10.2 mm. in the largest size class, and may 
be regarded as the probable upper limit since they ap- 
proach the queen which is 14.3 mm. (Wheeler). This in- 
crease over the 8 mm. linear dimension noted by Smith, is 
accentuated by the allometric growth in proportions of 
the head which accompany it, rendering the soldiers 
quite huge. The width of the soldier head varies from 
