i9ir).] 117 



point that is very raariced in the species of Enijdenrns. Specimens are 

 best cleaned by soaking in very hot water, then washing them with 

 soap and afterwards with benzine. 



The fine setae are a very unusual occurrence in water-beetles. As 

 already stated they occur only in some of the forms. In the Emideuri 

 there are numerous stubby bristles, as also pointed bristles and curved 

 stiff setae, but fine, flexible hairs are not to be found on any part of 

 the body in most of this group. The bristles and curved setae are 

 well known to entomologists, and are useful for distinguishing the 

 species. But the fine silky hairs have hitherto escaped attention, 

 except by Kuwert, who made use of them in so partial a manner as to 

 be very misleading : those on the legs he called swimming-hairs, though 

 it is not yet established that they have this function. One or two very 

 fine hairs exist at the front of the pronotum near the angles ; they are 

 very delicate and difficult to detect, being very collapsible, but in 

 Meghelophorus they can be found with comparative ease. Very long 

 fine hairs, one on each joint, exist on the hind tarsi of various forms 

 — TrichelopJiorus e.g. — the insertion being near the base, and near the 

 upper margin of the inner face of the foot. Those on the tibiae may 

 easily be found in H. laticoUis. It must, however, be admitted that 

 however important these fl.exile hairs may be, they are scarcely suitable 

 for systematic purposes at present, owing to the difficulty of their 

 demonstration. 



The abdominal pubescence or clothing will no doubt prove to be 

 important. Kuwert makes use of it in an unsatisfactory way in a few 

 cases, while Ganglbauer goes so far as to give a " thickU- pubescent " 

 abdomen as characteristic of all the Helofhorini. This, however, is 

 erroneous. If an ordinary form, e.g., Meghelopliorus aquaticns, be 

 examined there will be found to exist a complex clothing on the abdomen, 

 longish sub-erect hairs near the tip, marginal hairs on the hind-margins 

 of the segment, scanty depressed hairs scattered over the surface, and a 

 copious system of hairs so minute as to be difficult of definition with 

 even a fairly high power of the microscope : hence the surface appears 

 quite dull. Covered by the clothing there is an excessively minute 

 sculpture, varying much according to the species, but often itself making 

 the surface quite dull ; so that from complete dullness of the abdomen 

 we must not infer the existence of minute pubescence. Empleums 

 (Megempleurus) rngostis is instructive on this point. Of course we 

 must be sure that the example we have under examination is perfectly 

 clean ; and in the species just named we shall then find that there are 



