7i6 



ARTHROPODA 



coxa of the fourth leg much larger than those of the others. Scutum 

 ornamented. 

 Type. — Dermacentor reticulatus Fabricius, 1794. 



In 19 10 stiles classified the species of Dermacentor into four groups, accord- 

 ing to the microscopical structure of the stigmal plates in the adult. 



A. Adults with four longitudinal rows of large denticles on each half of 



hypostome, stigmal plate nearly circular without dorso-lateral 

 prolongation, goblets very large — D. nitens. 



B. Adults with three longitudinal rows of large denticles on each half of 



hypostome, goblets small, medium, or large. 

 Dorso-lateral prolongation of stigmal plate absent — Salmoni group. 

 Dorso-lateral prolongation of stigmal plate distinct. 



Goblets of medium size — Andersoni group. 



Goblets small — Reticulatus group. 



The Salmoni group includes D. alhipictus Packard, 1869; D. salmoni Stiles, 

 1910; and D. nigrolineatus Packard, 1869. 



The Andersoni group inolvides D. occidentalis Marx, 1892; D . parumapertus 

 Neumann, 1901; D. venustus Marx, 1897; andersoni Stiles, 1905. 



The Reticulatus group includes D. reticulatus Fabricius, 1794; D. variabilis 

 Say, 1 821, 



Remarks. — There has been the greatest confusion as to the tick 

 which causes Rocky Mountain fever. This was called Dermacentor 

 occidentalis because Stiles considered that D. andersoni Stiles, 1905, 

 was identical with D. occidentalis Marx, 1892, but the two forms 

 have since been shown by him to be quite distinct. Therefore in 

 any reference to a tick causing Rocky Mountain fever, no matter 

 what name is used, it is important to understand that D. andersoni 

 Stiles, 1905, is the species really referred to. 



Dermacentor reticulatus Fabricius, 1794. 



Synonyms.- — Acarus reticulatus Fabricius, 1794; Ixodes reticulatus 

 Fabricius, 1805; /. marmoratus Risso, 1826; Dermacentor alhicollis 

 Koch, 1844; D. pordalinus Koch, 1844; ^- ferrugineiis Koch, 1844; 

 Hcemaphysalis marmorata Berlese, 1887. 



Dermacentor with coarsely punctate stigmal plate. 



This tick gains its importance from the fact that for some time 

 it was considered to be the cause of the spread of Rocky Mountain 

 fever, which was really due to the nearly related D. andersoni, with 

 which it was long confused. It probably does not occur in America. 

 It is widely distributed through Europe and Asia. 



Dermacentor occidentalis Marx, 1892. 



This tick was received by Marx from Occidental in California, and was first 

 described by Neumann. It is found in the north-western portion of the 

 United States from California to Montana. 



Morphology.— Male : Oval, narrow in front, broad behind; scutum varie- 

 gated brown and white. Anteriorly there is an elliptical area, the pseudo- 

 scutum, closely representing the form and colour of the female scutum, and 

 limited by a white border, and possessing two lateral brown stripes, with a 

 median brown stripe or spots between them. Behind this there are four 

 brown stripes arranged in a curve, open anteriorly. Posterior to these usually 

 five brown stripes ; one central and two lateral. Between these areas the whole 



