COLEOPTERA. DYTICIDiE. 103 



genera given in my Synopsis is founded, and which appears more 

 natural than any previously proposed, by bringing together all the 

 small species without a visible scutellum, and by removing Pcelobius 

 to its legitimate station, as pointed out byLatreille, near to Colynibetes. 



Amongst the British insects of which the family is composed, the 

 genus Haliplus (^fig. 5. lO. H. elevatus) is distinguished by having the 

 maxillary and labial palpi (^ff. 5. 12. 13.) terminated by a short subu- 

 lated joint, and especially by the extraordinary dilatation of the pos- 

 terior coxae (Jig. 5. 11.). Some of the species of Hyphidrus and 

 Hydroporus vary considerably in the appearances of the sexes : their 

 variations have been generally regarded as specific distinctions ; thus, in 

 Hyphidrus ovatus, one of the sexes (Hyd. gihha Fabr.), has the elytra 

 sericeous, whilst in the other (ovalis Fab?-.) they are glabrous ; the in- 

 dividuals of the latter sex being also much larger than the former. 

 But a difference of opinion exists as to the precise sexes of these 

 respective individuals, Gyllenhal regarding the former as males and 

 the latter as females, and Erichson and Dejean maintaining a different 

 opinion. The larger size of the latter, indeed, leads to the supposition 

 that they are females, whilst, from analogy with the larger species of 

 the family, the glabrous elytra of the same individuals would indicate 

 the male sex ; and the anterior tarsi in these are dilated, whilst in 

 the others they are compressed ; the latter character is also found in 

 Hydroporus memnonius Nicol. (niger St., jugularis Bab.), and some 

 others, in which the sexes are similarly variable in the appearance of 

 the elytra ; but in these the sexes are of nearly equal size. 



Pcelobius Hermanni, a common species, is remarkable for the noise 

 which it makes when held in the fingers, by friction of its abdomen 

 against the elytra. 



Acilius sulcatus is another species which possesses the power of 

 making a noise. Frisch states that this is produced under water ; but 

 a specimen of the insect which I kept some time (and which I had 

 caught on the ground, having fallen whilst ffying upon some glass- 

 panes which it had evidently mistaken for water) was equally noisy 

 when confined in a box in the sunshine, making a loud humming for 

 a considerable time, without ceasing, and without my being able to 

 perceive the slightest motion of the abdomen against the elytra ; hence 

 I conjecture that it might be produced by the action of the air upon 

 the alulets, which is also the opinion of Dufour. This insect, more- 

 over, is able to leap to a considerable height, when laid upon its back, 



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