GEOGRAPHICAL DISTRIBUTION, 11 



as in this country. Two common tropical genera, Tlyalomma and 

 Afonomma^ have not yet been taken in this country. The two genera 

 of Argasidse favor warm countries. Two of the European species 

 occur in our country, doubtless from importations. Several other 

 European species have been accredited to the United States, but in 

 all cases through erroneous determinations. In the United States 

 the species of Rhipice/phalus and Margaropus are restricted to the 

 Southern States. Several species of Amhlyomma spread northward 

 along the coasts and up the great valleys. The species of Derma- 

 centor are more restricted in distribution, and more abundant in the 

 Noi'thwest. In Ixodes the western species are quite unlike those of 

 the East. One sj^ecies of Hcemaphysalis is widely distributed in this 

 country. Although a few species are as yet known from only one 

 host, it is improbable that any are confined to one species of animal. 

 Dermarenfor is usually found on large mammals and Ixorlcfi on small 

 mammals. 



ABUNDANCE. 



Dermacentor is our most common tick, and the males are about as 

 numerous as the females. RlripicepJialus and Margaropus are abun- 

 dant locally, but the males of Margaropus are not so often seen. In 

 Amhlyomma the males are slightly less common than females. In 

 Ixodes the males are comparatively rare, and in several species un- 

 known to me. One species in the South is quite abundant, but of the 

 other Ixodes only a few are taken at one time. 



HISTOKICAL. 



Since the group is of such great economic importance, the need of 

 a technical revision of the species is apparent. There has never 

 been such a revision of our species. Say described a few species in 

 1821, Packard several more in 1869, and Fitch in 1871. Koch, in 1844, 

 described a host of ticks from all over the world, naturally including 

 a few from the United States. Each of the authors worked inde- 

 pendently of the others. The late Dr. George Marx was much inter- 

 ested in this family of mites, and intended to monograph it, or at 

 least our native species. To this end he had prepared many fine 

 drawings and a considerable body of manuscript. I have had access 

 to this material, and can testify to its high scientific character. In 

 the genus Dermacentor^ for example, he had the forms known to him 

 separated out as I shall use them in this paper. Later Avriters con- 

 fused several of these species, which he rightly held to be distinct. 

 Doctor Marx's manuscript is not suitable for publication, being frag- 

 mentary and out of date, but many of his figures are so valuable that 

 I have added two plates made up of them. These of course should 

 be credited to him. 



