964 On Aquatic Carnivorous Coleoptero or Dytiscida. 



The group Vatellini is an aggregate remarkable aaiong the Dytiscidse from the 

 fact that the prosternal process does not connect with the metasternum, this is an 

 imperfection of stnictui'e 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 inasmvich 

 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 Dytiscidse ; 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 Dytiscidas, 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 m eta thoracic episttrnum 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 tar as is af present known, possessing 

 this peculiarit}' . 



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 ; 



