On Aquatic Carnworous Coleoptera or Dytiscide. 833 
structures of the two, just in that proportion has the theory of genetic relationship 
between them become incredible. Now as Pelobius stands in relation to Carabidee 
and Dytiscidee as Archeeopteryx does (or did) to birds and lizards, it is quite 
clear that most interesting fossil does not any more prove that birds are descended 
from lizards, than Pelobius proves that Dytiscidee are descended from Carabide, 
or Carabide from Dytiscidee. 
I. 2—Genus NOTOMICRUS. (Vide p. 260.) 
The four species forming this aggregate, are the most minute of the Dytiscide 
and among the smallest Coleoptera, the length attained being only about 1 m.m. 
The form is rather depressed, the surface extremely polished and shining, without 
punctuation or pubescence. The antennz have no thickening of the middle joints, 
and are short and simple. The anterior coxe are minute and placed at a considerable 
distance from the front of the thorax ; the prosternal process is quite small and is 
rounded behind. The anterior tibize and tarsi are simple, the former with scarcely 
developed spur, the latter with the basal joint not notably elongate. The breast 
is excessively polished so that no trace of the suture between the hind coxa and 
metasternum can be detected. The coxal processes are slightly prolonged towards 
their outer hinder angle, the coxal cavities are slightly separated, with the coxal 
notch very minute and narrow. The swimming legs are excessively feeble, and the 
hind tarsi are very slender, longer than the tibiz. 
The genus is readily distinguished by the simple anterior legs, by the obliterated 
suture between the coxa and metasternum, and by the very feeble swimming 
legs. I have not been able to see the palpi, nor to ascertain well the details of 
the structure of the tarsi. 
As it stands at present the genus is divided between Australia and South 
America; but possibly one of the two species from the latter locality may be found to 
be sufficiently different from the others to justify a new generic name being formed 
for it; it has the swimming legs much less elongate and slender ; other species will 
no doubt be discovered, and this may admit of the characters being correctly formu- 
lated. At present I cannot pronounce an opinion on the relations of this genus to the 
other genera of Noterini and I shall therefore leave it isolated in the second 
synthesis; I think it probable that this course will prove to be the natural one, 
even after the structure has been more completely ascertained, for I very much 
doubt whether it has any close approximation to Hydrocoptus, or any other form 
yet brought to light. 
