1954] Creighton and Gregg — Cryptocerus texanus 57 
casts considerable doubt on the statement made by Wheeler 
in 1917 (12) and repeated by Emery in 1920 (13) that 
the major Neotropical additions to our ant fauna are rela- 
tively recent. If this northward migration was, as these 
authorities suppose, post-Pleistocene (Emery admits the 
possibility that it may have extended back to the Pliocene) 
at least there has been time for the development of marked 
changes in the ecology of some of the migrant species. No 
other conclusion is possible in the case of Cryptocerus tex- 
anus and Pseudomyrmex apache. The environmental prefer- 
ence of both these species has altered from that of their 
tropical ancestors to the extent that now neither of them 
seems capable of life in the tropics. This may, of course, 
be a recent phenomenon but more likely it indicates a 
long residence in the areas that they now occupy. 
Literature Cited 
1. Smith, M. R., Proc. Ent. Soc. Wash. Vol. 49, No. 1, pp. 29-40, 1947. 
2. Smith, M. R., Psyche, Vol. 56, No. 1, pp. 18-21, 1949. 
3. Kempf, W. W. Revista de Entomologica, Vol. 22, Ease. 1-3, pp. 1- 
244, 1951. 
4. Kempf, W. W., Studia Entomologica, Petropolis, Brazil, pp. 1-30, 1952. 
5. Wheeler, W. M. Bull. Amer. Miis. Nat. Hist. Vol. 20, p. 104, 1905. 
6. Wheeler, W. M., Ants, Columbia Univ. Press, p. 304, 1910. 
7. Emery, Carlo, in Wytsman Genera Insectorum, Ease. 174, p. 305, 1922. 
8. Wheeler, W. M., Bull. Mus. Comp. Zool. Harvard, Vol. 90, No. 1, 
p. 210, 1942. 
9. Santschi, E., Ann. Soc. Cien. Argentina, Vol. 87, p. 10 (44) 1919. 
10. Gregg, R. E., Ecology, Vol. 23, No. 3, p. 299, 1942. 
11. Creighton, W. S., Psyche, Vol. 59, No. 4, p. 134, 1952. 
12. Wheeler, W. M., Proc. Amer. Acad. Arts Sci. Vol. 52, No. 8, p. 492, 
1917. 
13. Emery, Carlo, Reale Accad. Lincei, Series 5, Vol. 13, Ease. 6, p. 440, 
1920. 
