104 



Mr. F. Balfour-Browne on (he 



on tlie disc, even wlien examined under liioli magnification 

 (x 172). A few specimens from Silesia sent me by Herr 

 Ganglbauer were similarly sculptured. It seems, tlierefore, 

 that there are " insular " and " continental " types o£ female 

 in this species also. 



The Pkosterxum. 



The sculpture of the prosternum was relied upon by 

 Gerliardt, who separated //. ruJicoUis, hef/deni, horealis, and 

 immacnlatuSj as having a grooved or channelled prosternum, 

 from H.fluviatilis and fuhicoll is, as having a flat one. He 

 did not attempt to distinguish between the four species with 

 grooved prosternum on any peculiarities of the grooving, and 

 Wehncke similarly carries the matter no farther. Reitter (15, 

 p. 203, footnote) points out that the separation of species on 

 the ground of grooved or flat prosternum often fails, and 

 mentions that in II. holsaticus, Scriba, the male has a flat and 

 the female a grooved prosternum. He mentions that Seidlitz 

 and Ganglbauer have both avoided using the form of the 

 prosternum as a specific character, but he himself describes 

 its nature in several species. 



Fijr. 1. 



The_ prosternum undoubtedly varies considerably in its 

 shape in all the species, and is also somewhat variable in 

 sculpture ; but it is, nevertheless, sometimes useful as addi- 

 tional evidence in determining a species, if it is used with 

 caution. The grooving or channelling varies from a slight 

 depression in the anterior narrow part to a long, shallow, 

 narrow channel to the posterior end, and there is also 

 a further modification produced by the widening out of 

 this channel. We might describe four degrees of grooving. 

 The first is the minimum type : in the second the groove 



