204 Mr. J. O. Westvvood's JJescrijjtlon 



has been of great service in the classification of this family of 

 water-beetles, and contains numerous observations on the structural 

 distinctions between the sexes of the types of most of the genera 

 of which it is composed) having overlooked several of these dis- 

 tinctive marks. The anterior tibiae of the males are much dilated 

 and curved at the base, the inferior external margin from the 

 middle to the tip being flattened, the edges being ciliated and the 

 under edge near the tip and opposite to the large sucker being 

 furnished with a single spur, as represented in my Modern Classi- 

 fication of Insects (vol. i. p. 95, fig. 5, G). In this respect the 

 genus Dytlcus agrees with Cybister, and differs from Hydatlcus, 

 Eunectus, and Acillus. The anterior tarsi in this sex are termi- 

 nated by two spurs equal in size, and each wltli a small tooth at 

 the base within. In the female the fore tibiae are straight, not 

 dilated at the base, and furnished with two spurs at the tip. The 

 ungues at the extremity of the tarsi are scarcely smaller than, and 

 formed as in, the males. The middle feet have the ciliation, 

 calcarice and ungues equal and alike in both the sexes, the tibiae 

 having the upper edge strongly, and the inner scarcely, ciliated, 

 the calcariae of unequal size, and the ungues equal, with a small 

 tooth near the base of each. The hind feet are alike in both 

 sexes, except that in the males both the upper and lower edges 

 of the tibiae and tarsi are ciliated with fine yellow hairs, whereas 

 in the female the upper edge alone is ciliated. 



In Mr. Hope's insect the three basal joints of the anterior tarsus 

 on the right side are dilated, but these are not more than three-fifths 

 of their ordinary width, the joints are of nearly equal size and form, 

 being together a kind of five-sided figure. On the underside the 

 basal joint is destitute of cups, except one of moderate size and 

 imperfect structure at the internal angle, the second joint has 

 about four very small ones placed near the sides, but the third 

 joint is more copiously furnished with little cups, but not to the 

 extent nor of the size of the normal individuals ; moreover the 

 extremi'.y of each of the three joints is furnished on the underside 

 with a pair of short strong spines ; the intermediate tarsus on the 

 right side is of the ordinary masculine structure, except that the 

 three basal joints are narrower than those on the opposite side. 

 On the left side of the insect the anterior tarsus is nearly of the 

 normal form and structure ; the three l)asal joints are however not 

 so broad nor so uniformly oval as in normal specimens, and on the 

 underside the small cups are not so numerous nor so regularly 

 placed, especially on the internal part of the basal joint. The large 

 basal cup, and the moderate sized lateral cup, are of the ordinary 



