222 BRITISH TYBOGLYPHID^. 



constant; behind the fourth pair of legs it varies 

 widely according to the extent to which the eggs in the 

 abdomen are developed. 



This species may be known by the combination of 

 long palpal flagella and dentate mandibles with an 

 abdomen not bearing mammilliform elevations, or spatu- 

 late or leaf -like hairs on its dorsal surface. The 

 nearest ally probably is the Histiostoma fimetarium of 

 Canestrini and Berlese ;* but it is distinguished from 

 that species by its serrated (instead of knife-like) 

 mandibles ; its pyrif orm (instead of oblong) form ; its 

 strongly convex (instead of concave) hind margin ; by 

 the presence of two pairs of largish hairs on the 

 antero-lateral corners of the abdomen, and the much 

 greater size of the two pairs on or near the hind 

 margin. 



Colour, The body is almost colourless, but as seen 

 by reflected light on a dark ground it has a very 

 decided blue tinge in those parts which are not occu- 

 pied by excremental (urinary) matter ; except in the 

 middle along the course of the alimentary canal, where 

 a yellow tinge is usually visible, and this often spreads 

 further in the body ; both the blue and the yellow are 

 transparent. The body is, however, generally very 

 highly charged with the excremental concretions usual 

 in the genus ; they are very abundant in this species ; 

 so that the greater part of the body is occupied by 

 opaque white, chalky-looking masses which show clearly 

 through the cuticle, giving their own colour to the 

 body; the distribution of these masses is constantly 

 varying. 



Texture really smooth and even polished, but the 



* "Nuovi Acari," in ' Atti Soc. Yeneto-Trent,' 1881, vol. vii, p. 150. 

 Berlese says (' A. M. S.,' fasc. ix), but with a ?, that the hypopus of 

 this species is the Acarus acarorum of Linnaeus (' Syst. Nat.,' p. 2934, 

 No. 81) ; and he also says, without a ?, that it is the Hypopus julorum 

 of Koch ('D. C.,' fasc. xxviii, pi. xx) ; but subsequently (fasc. xxix, 

 No. 4) in the same work he gives Hypopus julorum, Koch, as a separate 

 species, which he afterwards (' A. M. S. Crypt.,' p. 186) identifies with 

 Histiostoma rostro-serratum, Megnin. See, however, Berlese's remarks 

 in his ' A. M. S. Notes,' fasc. iv, pp. 44, 45. 



