On Aquatic Carnivorous Coleoptera or DijtiscidcB. 851 



Middle coxse rather widely separated ; the intercoxal process of the metastenium 

 is slightly emarginate in front, in adaptation to the prosternal process ; the metaster- 

 num is elongate in the middle, and its side wings are extremely slender ; the hind 

 coxae are extremely large, their articular cavities are very widely separated, and 

 are quite exposed and unprotected, being placed quite outside of the broad coxal 

 processes which are adpressed to the level of the ventral segments ; the hind border 

 of the coxsB is completely soldered to, and amalgamated with the basal ventral 

 segment. The hind legs are rather slender, their tibiiB and tarsi not much ciliate, 

 the latter terminated by a stout short claw, (there exists a second claw, but it is so 

 short that it can only be detected by a most careful examination). On the inner 

 face of the wing-case the raised ridge has a very strong double wave near the 

 extremity. The anterior and middle tarsi are small, four-jointed, the third joint 

 bilobed, the fourth joint exserted, and of about the same length as each of the other 

 joints. 



Although these insects have hitherto been classed with the old world Hyphydri, 

 and not in any way distinguished therefrom, they are really widely different. The 

 soldered ventral segment is of great importance as a distinguishing character, but 

 besides that, the genus has the hind articular cavities more widely separate, and 

 the upper border of the coxas different in form ; the prosternum is still more 

 reduced, while its process is broader and larger, and the inter-coxalband is prominent; 

 the anterior tarsi are formed as in Hydrovatus, and very different from those of 

 Hyphydrus. External marks of the sexes are scarcely to be found, and the colour 

 of the upper surface is without the variegation existing in Hyphydrus. 



The Pachydri are peculiar to tropical America and the West Indian Islands. 



I. 21.— Genus DESMOPACHRIA. {Vide p. 340). 



About twelve species form this aggregate ; they are minute or small insects, of 

 short, broad form, convex beneath. Front of head margined, the clypeus overhang- 

 ing the labrum, but when viewed from beneath the latter is seen to be distinctly 

 exserted. Prosternum extremely minute, forming in fact merely a slender frame 

 for the coxge : prosternal process minute, rhomboidal, acuminate behind. Middle 

 coxae distinctly separated. Metasternum very long in the middle, with its curved 

 side wing excessively slender, so as to be a mere line, the suture between it and the 

 coxa is however excessively obliterated so that this character is not easily 

 appreciated. Hind coxse enormous, their processes quite adpressed to the ventral 

 segment, moderately broad, and leaving quite exposed the coxal cavities : hind 

 border soldered to first ventral segment. Hind legs moderately stout ; their rather 

 stout short tibiae of even thickness throughout. Front and middle tarsi small, fonr- 

 jointed, third joint but little lobed. Elytra on inner face at extremity with a single 

 prominent ligula. 



TRANS. ROT. DUB. SOC, N.S., VOL. II. 6 H 



