238 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



condition, Hydroporus gigas No. 427 (Chostonectes) may be mentioned. In Pelobius 

 and the Hydrovatini we have another form of articulation of ihe swimming leg -. 

 inasmuch as the coxal cavities are rather widelj^ separated, but yet are concealed 

 by a coxal lobe; the inner termination of the articular cavity appears therefore in 

 these cases in the form of an opening or excision on the hind margin of the internal 

 lamina. I have already spoken of a mark which commonly exists on the hind 

 margin of the internal lamina, either as a slight notch or interruption of the outline 

 of the coxal process (C^^bister, Ilybius, &c.,) or as a closed shoi't suture (Dytiscus). 

 This coxal notch is remarkably persistent, and indeed thougli it appears to be absent 

 in many forms (Acilius e.g.) yet on careful examination I have alwaj's found some 

 traces of it, it exists also in the Carabidse, and is perhaps an indication that this 

 part of the coxa is formed by the coalescence of two distinct pieces ; its persistence 

 is at any rate very remarkable, and is clearly an indication of some formerly different 

 structural condition of these parts. I had thought at first that the articular opening 

 existing in Pelobius and Hydrovatini was merely an enlargement of this coxal notch 

 but such is not the case, for in Pelobius the coxal notch may be seen existing on 

 the coxal process, just outside the articular opening. In the Noterides the coxal 

 lobes are of large size and peculiar form, reaching furthest backwards at their outer 

 angle, which is thus more or less acute, they are greatly prominent from the rest of the 

 under surface, and thus form a deep elongate axilla, while the articular cavities them- 

 selves are completely concealed ; in respect therefore of the development of the 

 coxal processes, and concealment of the articular cavities, the Hyphydrini and the 

 Koterides stand as the op^josite extremes of the family. In Amphizoa the articular 

 cavities are widely sejDarated, and are concealed, but their inner termination is 

 distinctly visible on the hind margin of the coxal process, the coxal notch being placed 

 immediately outside of this opening : this differs from the articulation in Pelobius, 

 inasmuch as the termination of the articular opening is not prolonged forwards, 

 and thus forms a shallow emargination instead of a deep excision, if we suppose the 

 space separating the two cavities in Amphizoa to be absent, the structure would 

 not then differ materially from what exists in the Macro-Dytiscidaj. 



The structure of the hind coxa in the Dytiscidse may be summed up as differing 

 from that of the Carabidce in the following points ; 1. The large size or area of the 

 external lamina ; 2. The arched anterior border of this part ; 3. The accurate adap- 

 tation and soldering of the two internal laminje together by a straight and perfect 

 suture; and 4. The contiguity of the articular cavities. As regards the first of these 

 points, it is certain that so far as the large majority of the Dytiscida3 are concerned, 

 the greatly increased size of the outer lamina of the hind coxa is very remarkable 

 and is one of the modifications of structure most characteristic of the family : it is 

 however only a question of degree, and varies extremely in the different groups, so 

 that Amphizoa and Pelobius, in which forms it is smallest, appear rather to be 

 Carabidaj than Dytiscidee in respect of this peculiarity : I am not aware however of 



