British Species of Haliplu?. 105 



extends from half to two-thirds of the way back along the 

 middle line^ while in the third it extends right to the poste- 

 rior end. The fourth is the extreme development of the 

 groove where it widens out, leaving nothing but a narrow 

 ridge on either side, and practically the whole width of the 

 prosternum is depressed. After an examination of a large 

 number of specimens, 1 have drawn up the following descrip- 

 tions of the 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 margins posteriorly are very slight and the groove is 

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

 side-ridges are almost obsolete. The line puncturation gives 

 the prosternum 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 {i. e. type 1, 

 see fig. 1 on opposite page), where the large punctures are 

 irregular in shape and give a corrugated appearance. The 

 "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 throughout (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 t^-^pe 2. 

 In both (J 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 large 

 scattered punctures. 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 (^ and ? . If, however, the 

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



H. ruficoUis. — The prosternum and its puncturation are 

 much the same as in U. wehnckei, but type 1 is, perhaps, the 

 most usual. Type 2, however, is not uncommon, and type 3 

 occurs, this apparently being more common on the contment. 



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

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

 H. riijicollis. 



H. immaculatus. — The prosternum usually distinctly chan- 

 nelled throughout its lengtii, and sometimes the posterior part 



