1977] 
Porter — Mesostenines 
81 
and Andean, reaching its austral limit in northern Argentina and 
including only three or four South American species. Trachysphy- 
rus, in contrast, has a big Holarctic fauna plus a massive endemic 
South American radiation of more than 150 species centered in 
mountainous and/or semiarid to arid parts of the southern half of 
the continent. Thus the Subandino has 21 Trachysphyrus, the 
Coastal Desert 12, but the Valley only one. Interestingly, the south 
Texan species, T. mesorufus, is a member of the Planosae group, 
the only Trachysphyrus stock of South American origin to have 
invaded Middle and North America. The heterogeneous distribu- 
tional patterns of Holarctic genera represented in the Valley show 
that this element has penetrated Middle and South America in 
different expansions at widely separated times. Trachysphyrus, 
because of its huge endemic South American fauna, probably had 
reached the southern continent by the middle or late Tertiary 
(Raven and Axelrod, 1975, p. 422 point out that even by the late 
Cretaceous the “northern Andes” were “beginning to approach 
their modern configuration” and thus could have served all through 
the Tertiary as a suitable habitat for temperate-adapted genera 
invading from the north.). The Transfuga group of Mesostenus, 
mainly Holarctic and in South America practically confined to the 
Andean region excluding Chile, doubtless moved south with Pleis- 
tocene glaciations. Finally, Gambrus, Trychosis, and Listrognathus, 
which only reach northern Mexico perhaps were pushed as far as 
the Valley only by the most recent and severest Wisconsin glacia- 
tion. 
Phaenology 
Hand collecting and Malaise Trap records of Lower Rio Grande 
Valley mesostenines obtained between June 1973 and March 1977 
are summarized in Table 1. 
Since hand collecting was possible only between 25 August-9 
September, 18 December-25 January, 11-12 March (1-8 April in 
1975) and 16 May-10 June, the data furnished in Table 1 show 
strong bias toward those periods. Fieldwork during February, 
October, and November, in particular, doubtless would have shown 
that these months have much larger mesostenine faunas than sug- 
gested in the table. Nonetheless, the phaenology emerges as uni- 
modal and invernal with an impressive peak that extends from 
December to March and includes 390 of the 679 specimens and 
