1977 ] 
Porter — Mesostenines 
89 
viduals among species, often referred to as evenness or equitability. 
As shown by the following data as to number of specimens col- 
lected and percent of total collection, the Valley mesostenine fauna 
has two extremely common species, six that may be considered 
moderately scarce, and 26 which are rare to very rare: 
1 . A. discoidaloides — 230 , 34 . 4 % 
2 . A. pertinax — 179 , 27 . 7 % 
3 . L. picta — 37 , 5 . 5 % 
4 . P. limitis — 34 , 5 . 1 % 
5 . C. texensis — 32 , 4 . 8 % 
6 . D. introita — 27 , 4 . 0 % 
7 . L. rufitibialis — 22 , 3 . 3 % 
8 . D. macula — 21 , 3 . 1 % 
9 . M. longicaudis — 11 , 1 . 6 % 
10 . M. agenioides — 10 , 1 . 5 % 
11 . M. discoidalis — 9 , 1 . 3 % 
12 . G. ultimus — 8 , 1 . 2 % 
13 . M. gracilis — 6 , 0 . 9 % 
14 . D. acadia — 5 , 0 . 7 % 
15 . L. cinctiventris — 5 , 0 . 7 % 
16 . P.fulvus — 5 , 0 . 7 % 
17 . D. sphenos — 4 , 0 . 6 % 
18 . L. orbus — 3 , 0 . 4 % 
19 . T. subgracilis — 3 , 0 . 4 % 
20 . D. pareia — 2 , 0 . 3 % 
21 . D. picta — 2 , 0 . 3 % 
22 . L. leucosoma — 2 , 0 . 3 % 
Each of the 12 mesostenines not listed above was collected only 
once during my five year survey, so that 35% of this community 
consists of very rare species. 
Partially similar equitability data emerge from my three year 
study of mesostenines in the northwest Argentine Subandino. Here, 
12 of the 33 species collected (36%) were represented by a single 
specimen each, so that the percent of very rare species in the Suban- 
dino and the Valley faunas is almost identical. However, of the 
other 21 Subandean species, two each accounted for 15% of the 
total number obtained, 1 for 11%, 1 for 7.1%, 1 for 5.9%, 2 for 
4.7% each, 1 for 4.1%, 2 for 2.9% each, 3 for 2.4% each, 5 for 1.8% 
each, and 2 for 1.2% each. The Subandean fauna thus has greater 
equitability than the south Texan in that specimens are apportioned 
more evenly among the commoner species. Here the two most 
abundant species, Trachysphyrus doddi and Basileucus sp., to- 
gether account for 26 specimens each or 30% of all specimens ob- 
tained, while the two most common Valley mesostenines make up 
62.4% of the total for their region. Moreover, mesostenines in gen- 
eral are much rarer in the Subandino than in the Valley. The entire 
Subandean sample was only 169 specimens (56 per year), while that 
from the Valley totalled 679 specimens (135 per year). Thus the 
Subandean fauna is numerically small and composed entirely of 
scarce to very rare species while the south Texas fauna is numeri- 
cally larger and contains several genuinely common mesostenines. 
