1903.] NATURAL SCIENCES OF PHILADELPHIA. 219 



The geographical distribution of the North American Leptothorax, 

 though very incompletely knoAvn, is not altogether devoid of interest. 

 So far as it is possible to generalize from existing data, it would seem 

 that the species are rather uniformly distributed over the entire con- 

 tinent, not excepting at least a portion of the Arctic regions. By this 

 I do not mean to say that the same species occur everywhere, or even 

 that the distribution of a particular species is very wide, but that the 

 ant-fauna of any given locahty usually comprises a few species of 

 Leptothorax. This indicates a wide range of adaptability to differences 

 of soil, moisture, temperature, vegetation, etc., within the same genus. 

 The extremes of this adaptation seem to be represented by forms like 

 L. curvispinosus, which inhabits the humid shady woods of the North 

 Atlantic States, and L. Pergandei, w^hich occurs even on the sun- 

 scorched soil of the Trans-Pecos deserts. 



We have few species in common with Europe, probably only L. 

 acervorum and L. muscorum, both presenting distinct American varie- 

 ties or subspecies analogous to and occurring over the same territory 

 as the American forms of Formica fiisca, rufa and sanguinea and Myr- 

 mica rubra. All of these forms occur far to the north and to consid- 

 erable altitudes, both in Europe and America, and undoubtedly 

 constitute important elements of an ancient palaearctic ant-fauna.^ At 

 lo.w altitudes and within our territory the forms of L. acervorum and 

 muscorum seem to be confined to the northernmost tier of States. 



The twenty species of Leptothorax recognized in the present paper 

 as occurring in America north of Mexico are about equally distributed 

 between the two divisions of the genus, which are characterized respec- 

 tively by the workers and females having 11- (the males 12-) jointed 

 antennae, and the workers and females having 12- (the males 13-) 

 jointed antennae. It is an interesting fact that the species with 11- 

 jointed antennae in the workers are mainly confined to the Northern 

 and Eastern States, those with 12-jointed antennae to the Western and 

 Southwestern territory. Exceptions are L. curvispinosus and acer- 

 vorum, which present varieties even in New Mexico (though at consid- 

 erable altitudes !) and L. tricarinatus , which was described from South 



1886, and III. Tomognathus sublajvis Mayr, ibid., Bd. XXI, No. 4, 1896; 

 Wheeler, "The Compound and Mixed Xests of American Ants," A7n. Natural., 

 Vol. XXXV, Nos. 414, 415, 417 and 418, 1901, and " Ethological Observa- 

 tions on an American Ant {Leptothorax Emersoni Wheeler)," Arch. j. Psych, u. 

 Neurol., Bd. II, Heft 1 u. 2, 1903 pp. 1-31. 



^ L. acervorum var. convivialis (q. v.) has been taken on the summit of Las 

 Vegas Range, N. M., at an altitude of 11,000 feet, by Prof. T. D. A. Cockerell 

 in xenobiosis with another boreal ant, Myrmica brevinodis. L. acervorum var. 

 Kincaidi was described by Pergande from Alaska. 



