474 Mr. G. R. Waterhouse's Notes on 



XXXVIII. Notes on Oinalium riparium, Homalota laevana, 

 H. dilaticornis and H. nigritula. By G. R. Water- 

 house, Esq., V.-P. Z.S., &c. 



[Read 5th January, 1863.] 



Omal'mm riparium, Thomson, Ofv. af Vet. Ac. Forh. 1856, 224, 3 : 

 Skandinaviens Coleoptera, torn. iii. p. 212, 3. — 1861. 



In average size this insect is a trifle larger than 0. rivulare : it 

 differs from that species in being ahiiost invariably of an uniform 

 pitchy black colour (elytra rarely piceous), with the exception of 

 the legs and one or two basal joints of the antennae, which are 

 rufous. The punctuation of the upper parts is rather less dense 

 and less strong. The foveae on the head are less strongly im- 

 pressed, and rather more widely separated, so that the mesial 

 raised area is broader ; the neck is dull, being distinctly aluta- 

 ceous, and has very few minute punctures, whilst the more glossy 

 neck of 0. rivulare has numerous strong punctures ; the antennae, 

 without being stouter, are rather longer. The thorax is broader, 

 and both the lateral and dorsal foveae are larger. In 0. rivulare 

 the lateral impressions extend forwards from the base to the 

 middle of the thorax, are glossy and strongly punctured, whilst 

 in O. riparium the corresponding impressions extend forwards 

 about two-thirds of the length of the thorax, are dull (being very 

 distinctly alutaceous), and present comparatively few small punc- 

 tures. Again, in 0. rivulare there is a groove containing a row 

 of strong punctures running parallel with the posterior margin of 

 the thorax, and between this and the margin itself is a glossy 

 ridge — neither the groove nor the ridge exists in 0. riparium. 

 Lastly, the elytra are longer, and have the external apical angle 

 more obliquely truncated. In most of the above points of dis- 

 tinction 0. riparium presents characters which approximate it to 

 0. Iceviusculum, but this last-mentioned species is larger, very gene- 

 rally has the thorax and elytra more or less pitchy — and not un- 

 frequently these parts are rufo-piceous ; its punctuation is very 

 decidedly finer and more scant; the thorax is distinctly dilated 

 in front (which is not the case in 0. riparium) ; the lateral 

 margins are sinuated behind so as to leave the posterior angles 



