On Aquatic Carnivorous Coleoptera or Dytiscide. 257 
little adapted for swimming organs, but both the inner and outer margins of the 
tibise and tarsi are abundantly provided with swimming hairs. In Amphizoa the 
hind legs are remarkable, inasmuch as they are completely destitute of ciliz or 
setee, and are elongate and slender, and not at all modified for swimming. 
Although the swimming legs of the Dytiscide in the higher forms are so remark- 
able and characteristic, yet there is not one of their many peculiarities sufficiently 
constant to serve as a character by which the family may be distinguished from the 
Carabidee : it is in fact only in the coxa that any peculiarity of structure can be 
pointed out as capable of serving as a test-mark for the family. It is true if 
Amphizoa were excluded from the Dytiscide, that we might define the family as 
possessing posterior tibize provided with elongate ciliz ; but then many species 
of Scarites in the Carabidee have the same parts quite as densely ciliate as have the 
Dytiscidee ; while if we try and seek for a character in any of the changes ot form 
and size of the various parts of the leg below the coxa, we find these to be so 
extremely variable as to be incapable of exact definition ; and if we descend to 
the feebler forms of swimming leg, and compare the leg of a Methles in the 
Dytiscidse with that of a Trachypachys, or of other Carabidee, we find it impossible 
to discover any difference of importance in the shape and form of the various parts. 
The phrase “ pedes natatorii” or “legs natatorial” commonly used as the definition 
of the family, is valueless for the purpose of a truly scientific taxonomy, although 
useful in conveying a vague general impression, as to one of the most marked 
peculiarities of the family as a whole. 
Il].—Tue Morpnoroaicat Speciric CHARACTERS. 
AP Jat 38, TR A IMLIL IG We ID AY ILS CIID An 
The Dytiscide are beetles, having the antennz eleven jointed, glabrous, and 
shining, entirely destitute of exserted setze or sensitive pubescence, and inserted on 
the inflexed margin of the side of the epicranium, very close to the eye, and quite 
close to the upper portion of the base of the mandible. 
The maxille provided with two elongate free lobes, the inner acuminate and 
curved at the extremity, ciliate or spinose along a portion of its inner margin, the 
outer slender, curved and palpiform, divided into two pieces by a transverse suture 
in all the species except those of the genus Amphizoa. 
The prosternum forming in the middle, behind, a process which projects 
horizontally backwards, behind the front legs, towards the metasternum. 
The hind coxee of large size, intimately soldered with, and appearing part of the 
* The abbreviated systematic characters in this part of the work are intended merely to serve as a 
guide in the search for particular species, and do not of themselves give a correct idea of the classification. 
adopted. ‘The definition of the family should form a part of the fifth synthesis, but is placed here for the 
convenience of those who have no knowledge as to what constitutes a member of the family. 
