A New Species of Hydracarina — Piersigia intermedia. 251 



XXIX.— Description of a New Species of Hydracarina— 

 Piersigia intermedia. By Wm. Williamson, F.R.S.E. 



(Received 12th February 1912. Read 26th February 1912.) 



For some reason, which is not apparent, errors have been made in the 

 description and figures of Piersigia limophila Protz, and these unfortunately 

 have found their way into works such as Piersig's " Deutschlands Hydrach- 

 niden " (Zoologica, Heft xxii.). A rectification of these, it is anticipated, 

 will appear before long, as the collections of Hydracarina made by Protz 

 are at present undergoing revision by Dv Karl Viets, of Bremen, to whom 

 I may here express my indebtedness for access to the type slides of Piersigia 

 limophila Protz and P. koenikei Viets. Although the first British specimen 

 of Piersigia differed in some measure from the then accepted type descrip- 

 tion and figures, it was recorded {Naturalist, 1903, p. Ill) as P. limophila 

 on the authority of the late Dr Piersig, who had by that time seen the 

 type and had agreed that it was inaccurately described. After a careful 

 examination of that specimen, as well as of later material, I find that the 

 British specimens possess characters distinguishing them from P. limophila 

 and P. koenikei, and as they appear to represent an intermediate form, I 

 propose to describe them as P. intermedia mihi. In comparison with the 

 other two species, I have observed that in a great measure the dorsal 

 surface of the new species resembles that of P. koenikei, and the ventral 

 surface that of P. limophila, and that while the genital acetabula of these 

 species appear to possess rather cylindrical stalks, the acetabula of the 

 new species are pyriform. 



Noticeable features, of the specimens of Piersigia which I have seen, 

 are the length of the gland orifices partially protected by the porose plates, 

 which are very conspicuous especially towards the body margin, and the 

 rather constricted appearance of the third segment of the first three pairs 

 of legs. 



Piersigia intermedia nom. nov. 



Syn.— 1903. Piersigia limophila, C. F. George, "Naturalist," pp. Ill, 112, figs. 1-8. 



Female : Body. — Elliptical, dorso-ventrally compressed. Length, 2"40 mm. ; 

 breadth, T92 mm. Colour scarlet with dark patches on the dorsal surface ; 

 legs a little paler than the rest of the body. Skin finely ridged, with 

 a sub-cuticular network of chitinous threads. Palpi, legs and epimera 

 porose. 



VOL. XV III. Y 



