68 



REPORT 108, U. S. DEPARTMENT OF AGRICULTURE. 



virulent in part of Montana. The late Dr. Ricketts proved that this tick was the 

 vector of the disease. The tick is colored much as our common dog tick (D. variahilis), 

 but the stigmal plate is very coarsely granulated. 



D. alhipictus Packard (fig. 117) is common in the Northern States on moose, deer, 

 cattle, and horses. It is more elongate than our other species of the genus, and the 



Fig. 127.— Head of Ixodes. 

 (Author's illustration.) 



Fig. 128.— Leg I of Ixodes: Section through, tarsus; 

 h, Haller's organ. (Author's illustration.) 



stigmal plate has no projection at the end; this species and D. nitens do not drop from 

 the host for molting. 



D. nitens Neumann occurs in Texas and the West Indies, -where it especially attacks 

 horses. The shield has no markings and the stigmal plate has only a few (4 to 10) large 

 rounded granules, and the palpi are shorter than the hypostome. 



Another species, D. hunteri Bishopp, related to D. venustus, occurs in Arizona. The 

 genus is not so well represented elsewhere in the world as it is in North America. 



Of Rhipicephaliis (figs. 119, 120) there are a great number 

 of species, most of which occur in Africa; several of the 

 South African forms have been connected with disease. They 

 occur in great numbers on the host, one of them, R. pulchellus 

 Gerst. (fig. 121), is very strikingly marked with red-brown 

 and white; it is especially common on the zebra and Cape 

 buffalo. R. sanguineus Latr. (fig. 118) is a reddish species, 

 often infesting dogs, and occurs in many warm countries, 

 including Texas and the West Indies. African coast fever 

 (produced by Theileria parva) is said to be spread by five 

 different species of Rhipicephalus, but R. appendiculaius 

 Neumann is the principal vector of the disease. A minute 

 hymenopterous parasite has been bred by Hunter and Hooker 

 from Rhipicephalus in Texas and was described by Dr. How- 

 ard as Hunlerellus hookeri; it occurs also in South Africa. 



The genus Rhipicentor has only a few species in Africa; 

 they resemble Dermacentor, but have the structural charac- 

 ters of Rhipicephalus. Their coxae are heavily spined, and 

 there are spines on the hind border of the capituhim. 

 The genus Aponomma is closely related to Amblyomma. The species are most 

 abundant in the Australian region, India, and Insulinde. A. gervaisi Lucas, a common 

 form, infests tortoises; it is brown, with three greenish spots on the scutum. Some 

 species found on snakes were put in Ophiodcs, but these are now kept in Aiuhlyomnia. 

 The genus Eschatocephalus {llaemalastor) occurs on bats in Europe, especially in 

 caves. Several species are known; all have the legs more elongate than in other 

 Ixodidie. 



Of Amhb/ojnma (figs. 124, 125) there are o\ or a hundred species; they are especially 

 abundant in the tropics. A. americanum J Ann. (fig. 122) is often found on cattle in the 

 Southern States and is called the "lone-star t'ck " on accoiint of the prominent yellow 

 spot at the tip of the scutum of the female. The male is very much smaller and has 



Fig. 129.— Shield of Ixodes 

 scapuZaris, female. (Orig- 

 inal.) 



