840 On Aquatic Carnivorous Coleopiera or Dytiscidie. 



group of prominent cilise ; the tarsi are as long as but much more slender than the 

 tibial : the middle leers also are a s^ood deal incrassate and laminate. 



These insects are distributed over a broad zone of the tropics extending from 

 Northern Australia, through the Indo-Malay region, Madagascar and tropical Africa, 

 to America, and in this latter part spread northwards to the United States, where a 

 species is found even so far north as Massachusetts. The Australian species is 

 decidedly a lower, or less evoluted form than any of the others. 



I. 1 1.— Genus MACRO VATELLUS. ( Vide p. 282.) 



This aggregate consists at present of seven species. They are insects of rather 

 elongate form, and equal in size the largest Hydroporini, attaining 7 or 8 m.m. of 

 length ; the outline of thorax and elytra is very discontinuous, the colour is obscure 

 and scarcely variegate, the upper surface is very densely punctured. The prosternal 

 process is broad and very abruptly bent, and terminates in a point which is concealed 

 between the front of the middle coxse ; these latter are perfectly contiguous, and 

 the mesosternal fork cannot be perceived. The mesosternum is placed at a very 

 obtuse angle with the metasternum, so that it is extremely exposed, between the 

 pro thorax and metasternum ; the posterior coxae are large ; the coxal lines are 

 divergent and widely separate in front, but approximate behind, they do not extend 

 quite to the apices of the coxal processes, and their indistinct terminal portion is 

 quite evidently turned outwards, and the coxal borders are much prolonged in the 

 transverse direction ; the posterior trochanters and venti'al sutures are nearly 

 normal : the suture between the second and third segments is not quite obliterated 

 in the middle. 



The sexual differences seem to be very slight. 



The species are found only in the warm parts of the New World, and are 

 extremely rare in collections. 



I. 12.— Genus VATELLUS. {Vide p. 285.) 



This is an autogenus; the insect is of Hydroporoid form, but with very dis- 

 continuous outline, and very elongate anterior tarsi, it is of obscure colour, with 

 very densely punctate upper surface. The prosternal process is rather elongate, and 

 is abruptly bent, and terminates in a point concealed between the fronts of the middle 

 coxae ; these are quite contiguous and exposed ; the mesosternum is placed at a very 

 obtuse angle with the metasternum, and in consequence is largely visible between 

 the prothorax and metasternum; the hind coxae are large, the coxal lines are rather 

 strongly elevated, a good deal divergent in front, approximate behind, and extending 

 quite to the extremity of the coxal processes, and not turned outwards ; the coxal 

 border has a large extension in the transverse direction, though very short longi- 

 tudiiiivlly. The posterior trochanters are thick and globular at their extremity. 



