Dritish Species of lli\\i[>]\i='. 1().> 



extenfls from half to two-tliirds of tlic \v;iy back along tlio 

 nruldle line, while in tlie thirtl it extends right to tlie j)Oste- 

 rioi- ond. The fourth is the extreme development of the 

 groove where it widens out, leaving nothing but a narrow 

 ridge on either side, and praetically the whole widtli of the 

 prosternum i.s depressed. After an examination of a large 

 number of speeimons, I have drawn up the following descrip- 

 tions of tlie prosternum : — 



H. apicalis. — The prosternum is sparsely covered with 

 large punctures, but closely covered with fine and very 

 distinct ones. The grooving is of the fourth type ; the two 

 raised marj;ins posteriorly are very slight and the groove is 

 very " flat-bottomed/' sometimes being so shallow that the 

 side-ridges are almost ob.^olete. The tine ])uncturation gives 

 the jn-osternum a somewhat dull appearance, which is a fairly 

 reliable characteristic for this species. 



H. fluviatilis. — The prosternum is flat, with sometimes a 

 tendency to grooving in the anterior narrow part (/. e. type 1, 

 see fig. 1 on oj)])osite page), where the largo punctures are 

 irregular in shape and give a corrugated appearance. Tlie 

 " process" or posterior region has large punctures, scattered 

 and so far apart that the whole surface appears smooth and 

 shining. 



H. nomax. — The prosternum is sometimes very faintly 

 channelled thioughout (type 3), but often the insect has to 

 be turned round in all directions, so as to get the correct 

 illumination to see this. Often the channelling is of type 2. 

 In both cJ and ? large scattered punctures occur, and the 

 interspaces are filled with fine puncturation ; but this seldom, 

 if ever, causes the prosternum to appear in any way dull. 



H. wehnckei. — The prosternum is shining and with largo 

 scattered ])unctures. Usually of type 3, though many 

 examples of type 2 occur and some specimens are of type 1, 

 Occasionally the width of the groove is increased, so that 

 type 4 is approached. Among the large punctures is a very 

 feeble fine puncturation in both (J and ?. If, however, the 

 groove is deep, the fine puncturation is usually distinct in it. 



H. ruficoUis. — Tlie prosternum and its puncturation are 

 much the same as in //. wehnckei, but type 1 is, ])erha|)S, the 

 most usual. Tyj)e 2, however, is not uncommon, and typo 3 

 occurs, tills apparently being more common on the continent. 



H. heydeni. — So far as my experience of this species goes, 

 I can find no difference as to the prosternum between it and 

 U. 7'np'roUis. 



H. immaculatus. — The prosternum usually distinctly chan- 

 nelled tluuugliout its length, and sometimes the j)osterioi- part 



