On Aquatic Carnivorous Coleopteixt or Di/tiscidce. 907 



approximation to Agabus is undoubted, but the form of the prosternal process, and 

 the ciliation of the hind margins of the swimming tarsi are quite those of Hydaticus, 

 while the style of colour is quite foreign to Agabus. There is no reason therefore 

 to look on the insect as in any respect a connecting link between Hydaticus and 

 Agabus, nor as having any genetic connection therewith ; it is really and truly a 

 Hydaticinid, having some parts of its structure approaching to the structure of the 

 like parts of Agabus. We may interpret tliis as an indication that it has had an envi- 

 ronment, at certain periods of the history of the species, like that of Agabus, but that 

 on the whole the environment of the ancestry has not been dissimilar to that of 

 Hydaticus. 



Although it must be considered as on the whole a lower form than Hydaticus, it 

 does not display any special relations with the lower species of that aggregate : 

 thus the lower species of Hydaticus have the eyes peculiarly small, while Prodaticus 

 pictus has them larger than even the higher Hydatid ; while its peculiarities of 

 colour and form are not in the least approximated by the lower Hydatid ; thus, 

 although it must be considered the lowest form of Hydaticini yet brought to light, 

 it displays no affinities whatever (except those of less evolution) witli the next 

 lowest forms of existing Hydaticini, and does not tend to suggest any descent from 

 a common ancestor. 



It is worthy of remark that the colour is spot for spot the same as that of the 

 North Australian Sandracottus guttatus. 



Tlie insect is found in Persia or Northern India, a region lying between the 

 region of Agabus, and a region where Hydaticus has a great development. 



I. 08.— Genus HYDATICUS. ( Vide p. 648.) 



This aggregate consists of about forty-five species, whose individuals are of 

 moderate size (one-third to two-thirds of an inch in length), of perfect form, with 

 impunctate or polished surface, and Avitli the upper surface variegate with black 

 and yellow (only one or two exceptions.) The head has the antennal portion 

 of moderate size or much reduced ; the eyes moderately large ; the prothorax is 

 without lateral margin. The anterior legs are separated by a rather broad space, 

 and the prosternal process is distinctly but not greatly broader than this space, and 

 is obtuse or rounded at the apex. The hind coxa is rather large, its front border 

 is never very near the middle coxa : the coxal lines are quite distinct, and are only 

 moderately turned outwards in their hinder portion, but mark off a broad supra- 

 articular border, the coxal lobes are of about equal development in the transverse 

 and loncritudinal directions ; there is a miimte coxal notch. The swimming legs 

 are highly developed, their terminal claws are nearly straight and the inner one is 

 elongate, about twice as long as the other ; the upper face of their tibia has a series 

 of large punctures, each of which bears a thick furcate seta, this series 

 of punctures (in order to view which the marginal cilise must be elevated) extends 



TSANS. BOT. DUB. SOC, M.S., VOL. II. 6 A 



