38 STUDIES ON ACAEF. 



1-6 a. DEMODEX NANUS, Hirst, 1918. 

 Ann. Mag. Nat. Hist. (ser. 9) vol. ii. 1918, p. 146. 



? . A minute but fairly wide form much like that present in Sorex 

 araneus castaneus. Length about .3^ times the width of the cephalo- 

 thorax. Abdomen usually considerably shorter than combined length 

 of cephalothoras and capitulum, but in one specimen it is longer. 

 Capitulum usually much wider than long; the spines on its surface 

 apparently obsolete or absent. 



Female. 



Total length (inch capit.) 87-102 /a 



Length of cephalothorax + capitulum ... 48 /a 



„ abdomen 39-55/1 



Greatest width of cephalothorax 24—31 /a 



„ „ abdomen 22 /a 



„ ,, capitulum (at base) ... 17 -21 ft 



Length of capitulum 13-14 /a 



Host : Black Eat (Eattus rattiis) and Brown Eat {Itattus norvegicus). Several specimens 

 collected from freshly killed rats by the author. 



Note. — Hahn has already described a species of Demodex (D. ratti) from a house 

 rat said to be Mus rattus. I have not been able to consult his original description, which 

 is referred to by Gmeiner. The latter says that the species is similar to that of the dog. 

 From this one would infer that it was an elongated form of comparatively considerable 

 size similar to that found in Eattus norvegicus. It is probable, indeed, that the rat from 

 which Hahn's specimens were taken was really Rattus norvegicus, the Brown or Norwegian 

 Eat (syn. Rattus decwnanus). I have only found specimens of the short form described 

 above in Black Eats, but both this form and the elongated form described under the name 

 D. ratti (see p. 37) are found in the Brown Eat, which thus certainly harbours two 

 distinct species. It is, of course, possible that both forms also occur in the Black Eat. 



The following species or varieties have not been examined by the 

 author : — 



14. DEMODEX CAPR^, RaiUiet, 1895. 

 D . folliculorum var, caprce, Railliot, Zool. M^d. Agric. 2nd Edit. 1895, p. 638. 

 According to Railliet the cephalothorax + capitulum of B. caprce 



together are almost equal to half the total length of the body. He 

 gives the following measurements : — 



Female. Male, 



Total length 230-250 /x 220-230/* 



Width G0-65/X 50-55 /a 



Ova ellipsoid (length 08-80, width 32-45 /x). 



Host: The Goat (Capra Jiircus). 



