964 On Aquatie Carnivorous Coleoptera or Dytiscida. 
The group Vatellini is an aggregate remarkable among the Dytiscidee from the 
fact that the prosternal process does not connect with the metasternum, this is an 
imperfection of structure found only elsewhere in a few of the Hydroporides. There 
are only about a dozen species known, distributed in three genera peculiar to South 
America. 
The Laccophilini differ curiously from the other Dytisci fragmentati inasmuch 
as the numerous species form a single genus, and this, plus a single autogeneric 
species, forms the entire aggregate ; the aggregate is a very highly evoluted one, 
the Laccophilini being in fact amongst the most perfect of the Dytiscidee ; we have 
then in this group a very highly evoluted form of which no less evoluted forms are 
known to exist, but as such must have existed formerly, it appears probable that 
the primitive Laccophilini were amongst the earliest organized Dytiscide, that their 
organization was inferior to that of more modern competitors, but that when these 
arose the higher Laccophilini in possession were able to hold their own, but that 
the more inferior forms became extinct. 
It is worthy of remark that in the Laccophilini the process of the epimeron that 
separates the metathoracic episternum from the coxal cavity is very small and the 
cavities are very perfectly formed ; and also that in it the epimeron is largely deve- 
loped at the episternal angle so as to be triangular in shape, whereas in the No- 
terides and Pelobius it is sublinear. 
The Dytisci fragmentati are distributed over all the warm and temperate parts 
of the world except the Polynesian islands and New Zealand, whence none are known. 
IV. 2.—Dytisci complicati. 
This extensive aggregate consists of about one thousand species, arranged so as 
to form three complex aggregates of the third, plus two aggregates of the second 
degree, and two isolated genera. These insects are united into one whole by the 
fact that the metathoracic episternum penetrates as far as the middle coxal cavity 
and so intervenes between the extremity of the mesothoracic epimeron and the side 
wing of the metasternum and prevents any actual contact between these two parts. 
This character is one of extreme importance, for it is only in these beetles that, so 
far as is known, such a structure occurs ; in all the vast mass of species forming the 
order Coleoptera these are the only ones, so far as is at present known, possessing 
this peculiarity. 
The character too is of complete constancy in the series ; I have not been able to 
detect any exception to it, and in certain cases where it at first sight appears doubtful 
whether the front side piece of the metasternum does reach the cavity or not, a 
more careful examination settles the point very decidedly ; a remarkable instance 
of this is afforded by Colymbetes. The part of the episternum which in the Dytisci 
complicati reaches the cavity is its peculiar, exposed and thickened anterior edge ; 
