922 On Aquatic Carnivoro^is Culeoptcra or Dyiiscid(£. 



quite contiguous, there beino- no inter-coxal prolongation of the front of the meta- 

 sternum. The aiesosternum is more or less exposed between the metasternum and 

 prothorax. The hind coxae are large, their front border has a considerable extensioii 

 in the anterior direction, and its most forward point lies very near the outside of the 

 body. The hind coxal cavities are not contiguous; and the swimming legs are slender. 

 The front and middle tarsi are peculiar, the three basal joints are elongate, more 

 or less compressed laterally, the third joint is scarcely bilobed, but has an emargina- 

 tion at the apex, in which is inserted the fourth joint, the terminal joint is therefore 

 exserted, it is not very long, but is very slender, and is terminated by two very 

 small claws; at the base of this (truly the fifth joint), the true fourth joint may be 

 detected, although it is very small and minute ; the joints of this tarsus ai'e very 

 loosely articulated, so that the foot has a very fragile apjiearance ; there is in some 

 species a good deal of sexual disparity in the structure of the tarsi, and in the 

 males of some species of Macrovatellus, the peculiar form of the tarsus is little 

 apparent, and departs but little from what exists in the Hydroporini. 



The three genera when examined are found to be very distinct inter se, Derova- 

 tellus is a small insect, Hydroporoid in form, and has the mesosternum but little 

 exposed, the head is very short in front, and has no anterior band inflexed over 

 the labrum ; its head is in fact Hydroporoid, while in Vatellus this part is more 

 Hyphydroid, there being an inflexed anterior edge placed at right angles to the 

 plane of the upper surface ; this genus, Vatellus, is highly remarkable on account 

 of the deep sutures of the ventral segments. 



In Macrovatellus the individuals are of comparatively large size, and the front 

 tarsi are not so slender as in the other two aggregates, while on the other hand 

 in it the exposure of the mesosternum reaches its maximum; in respect of its head 

 and the posterior coxal cavities, it may be considered as intermediate between 

 Vatellus and Derovatellus. 



The Vatellini form a very natural and interesting aggregate ; although on account 

 of the structure of the intermediate coxal cavities the group belongs to the Dytisci 

 fragmentati, yet it has no other relationship with the components of that series ; 

 it may be considered to be the analogue in the Dytisci fragmentati, of the 

 Hydroporides in the Dytisci complicate The Vatellini show in fact several points 

 of approximation to the Hydroporides, but these approximations are to different 

 members of that tribe, not to any one form thereof, and the approximation is never 

 in a number of characters, but only in a single point. Thus the peculiar prosternal 

 process not connecting with the metasternum, reappears in Bidessini (Tyndalhydrus) 

 and in Hyphydrini (Andex). The peculiar tarsi are somewhat similar to those of 

 Hyphydrus very much elongated, and this point is also approximated to some 

 extent by Necterosoma of the Hydroporini. The widely different and isolated 

 Sternopriscus approximates the Vatellini by the exposure of the mesosternum. 

 One of the most pecuhar of the European species of Hydroporus (Dytiscus dorsalis 



