1915.] 235 



classifying the species of Helo)/horns, for the various forms are not 

 divisible into two groups on it, the conditions being really more com- 

 plex than I have mentioned ; sometimes the shoulder is visible as stated 

 above in H. aeneipennis, while in others it is not, H. mimitus 

 (= griseiia). My definition as to visibility of the flanks applies, there- 

 fore, only to the portion outside the metasternum, not to the portion 

 outside the mesosternum. Moreover, the amount of visibility of the 

 flanks differs in the various species in which it is present, being much 

 in H. nanus and championi and only little in H. mulsanti. 



Another character that is of importance in recognising the species 

 is the length of the maxillary palpi. This has been used for formally 

 tabulating tlie species by Seidlitz in his "Fauna baltica'': unfortu- 

 nately, however, this character is subject to sexual difference, the palpus 

 being frequently longer in the male than in the female of the same 

 species, and also, as has been already remarked by Rey, being somewhat 

 variable even within the one sex. 



The form of the channel on the head appears to me to be on the whole 

 the best for primary division of the genus, though it must be admitted 

 that the distinction is not very great, and is in some cases difficult 

 of appreciation, especially if the head is not well extended from the 

 thorax. 



Some of the characters made use of by Kuwert are fictitious, 

 depending on whether the specimen is thoroughly cleaned or not. 



To satisfy myself as to the reality of the species distinctions I 

 have made several hundred dissections of the genital structures, and 

 there is no doubt that these afford the most certain characters, 

 although the differences are but slight, and are subject to a certain 

 amount of variation — or, perhaps, apparent variation — arising from 

 maturity or immaturity and from differences in attitude of the parts. 



In addition to the remarks I have already made as to the 

 aedeagus (ante, pp. 27-30) I must make a further explanation. 

 The basal piece (bp) is to some extent elastic, and very much so 

 when not quite mature. It, therefore, may be made longer or shorter, 

 according to the tension it is subjected to. The median lobe (nil) 

 is connected with the lateral lobe by a sort of gusset, and according to 

 whether this gusset is extensively or minutely membranous depends 

 the amount of protrusion of the lobe. In fully mature specimens 

 the amount of possible protrusion is but slight, while in immature 

 individuals it is greater, but never is it very great. The length 



