1977] 
Porter — Mesostenines 
79 
Note that all these genera except Biconus, Cyclaulus, Basileucus, 
and Baltazaria are shared with the Valley. A simple index of af- 
finity (Odum, 1971, p. 144) thus gives 0.606 (out of a possible 
1.000) as the degree of similarity between the Valley and Coastal 
Desert mesostenine faunas. Actually, the real value probably ap- 
proaches 0.777, since four more Valley genera ( Cryptanura , Bi- 
cristella, Mallochia, and Pachysomoides ) occur also in the Ecua- 
dorian rainforests and Andean cloud forests, so that they very 
likely penetrate the northern fringes of the desert. 
The northwest Argentine Subandino of Salta, Tucuman, Cata- 
marca, and La Rioja provinces resembles the Valley because it is 
in subtropical latitudes where many Neotropic taxa approach their 
distributional limits. However, the Subandino differs from the 
Valley by its inland location and relatively high altitude (study 
sites between 900 and 2000 m.). Thus it has a much cooler tem- 
perature regimen that includes frequent winter frosts (annual aver- 
age temperature 13-15.5 degrees C. vs. 23.4 degrees C. for the 
Valley). Moreover, the Subandino is a genuine semidesert with 
only 80-250 mm. of rain per year (vs. 669 mm. for the Valley). 
Three years’ use of 10 Malaise Traps and frequent collecting 
trips at all seasons between 1966 and 1972 obtained from the 
northwest Subandino a mesostenine fauna of 10 genera and 33 
species, including seven Neotropic taxa ( Dotocryptus , Diapeti- 
morpha, Basileucus, Polycyrtidea, Polycyrtus, Messatoporus, and 
Agonocryptus ), two Sonoran genera ( Compsocryptus and Meso- 
stenus of the Longicaudis group), and two Holarctic genera (Tra- 
chysphyrus and Mesostenus of the Transfuga group). Considering 
Polycyrtus almost certainly present in the Valley (it is in the east- 
ern U.S. and northeast Mexico), we get for the Valley and the 
Subandino a similarity index of 0.580, one surprisingly high for 
two localities separated by about 42 degrees of latitude. In fact, 
since the Valley genera Cryptanura, Bicristella, Mallochia, Pachy- 
somoides, and Joppidium reach at least the borders of the Suban- 
dino in northwest Argentina, the index of similarity eventually 
could prove as high as 0.8000. 
With regard to the Neotropic element, the above comparison of 
south Texas, coastal Peruvian, and Subandean mesostenines, only 
reemphasizes the vast South and Middle American distributions of 
so many of these genera. Species, of course, differ widely from 
place to place but at the generic level we find remarkable similarity 
