840 On Aquatic Carnivorous Coleoptera or Dytiscide. 
group of prominent cilize; the tarsi are as long as but much more slender than the 
tibia ; the middle legs also are a good 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. 11.—Genus MACROVATELLUS. (Vide p. 282.) 
This aggregate consists at present of seven species. They are insects of rather 
clongate 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 coxze; 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 
prothorax and metasternum; the posterior cox 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 ventral 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. 
J. 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 
coxa; 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 coxee are jarge, 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 lias a large extension in the transverse direction, though very short longi- 
tudinally. The posterior trochanters are thick and globular at their extremity. 
