14-2 PARASITES OF THE DOMESTIC ANIMALS 



the capitiiluin, which is terminal and not upon the ventral face of the 

 cephalothorax as in the Argasidse. Sexual dimorphism is marked, the 

 dorsal surface of the males being almost covered by the scutum. In 

 the distended female the scutum appears as a small shield directly be- 

 hind the capitulum. Only the females are capable of great distension. 

 The spiracles are posterior to the fourth coxae. The eyes, if present, are 

 situated laterally upon the scutum. 



Nine genera have been described under the famity Ixodidae, as fol- 

 lows: Ixodes, Hsemaphysalis, Dermacentor, Rhipicentor, Rhipicephalus-, 

 Margaropus, Boophilus, Hyalomma, and Amblyomma. 



Four of the above, — Ixodes, Dermacentor, Margaropus, and Am- 

 blyomma, — -contain species occurring upon cattle and other animals in 

 the United States. The generic characteristics of these are given by 

 Nuttall and Warburton (A Monograph of the Ixodoidea, 1911) as 

 follows: 



1. Ixodes. — Inornate, without eyes and without festoons; spiracles 

 round or oval; palps and basis capituli of variable form; coxae either un- 

 armed, trenchant, spurred, or bifid; tarsi without spurs. Sexual di- 

 morphism pronounced, especially with regard to the capitulum. In 

 the male the venter is covered by non-salient plates: one pregential, 

 one median, one anal, two adanal and two epimeral plates. Anal groove 

 surrounding anus in front. 



2. Dermacentor. — Usually ornate, with eyes and festoons; with 

 short, broad or moderate palps and basis capituli rectangular dorsally. 

 In some species coxae I to IV of the male increase progressively in size; 

 in all species coxa IV is much the largest ; the male, moreover, shows no 

 ventral plates or shields. Coxa I bifid in both sexes. Anal groove con- 

 touring anus behind. Spiracles suboval or comma-shaped. 



3. Margaropus. — Inornate, with eyes, but without festoons, with 

 short palps and capitulum intermediate between that of Rhipicephalus 

 and Boophilus; highly chitmized; the unfed adults of large size. The 

 female with very small scutum. Coxae conical, unarmed but for a small 

 spine posteriorly on coxa I. The male with a median plate prolonged 

 in two long spines projecting beyond and to either side of the anus; 

 with coxae similar to those of the female; legs increasing progressively 

 in size from pair I to IV, the articles, especially of leg-pair IV, greatly 

 swollen. When replete, the male shows a caudal protrusion. Anal 

 groove obsolete. Spiracles rounded or short oval in both sexes. 



4. Amblyomma. — Generally ornate, with eyes and with festoons. 

 With long palps; of which article II is especially long, basis capituli of 

 variable form. The male without adanal shields, but small ventral 

 plaques are occasionally present close to the festoons. Anal groove 

 contouring anus behmd. Spiracles subtriangular or comma-shaped. 



Six species are found upon cattle and other domestic animals in this 



