On Aquatic Carnivorous Coleopfera or Dijtiscid(p. 257 



little adapted for swimming orgacs, but both the iuner and outer margins ot the 

 tibiae and tarsi are abundantlj'- provided with swimming hairs. In Amphizoa the 

 hind legs are remarkable, inasmuch as they are completely destitute of ciliee or 

 setse, and are elongate and slender, and not at all modified for swimming. 



Although the swimming legs of the Dytiscidse 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 

 Carabidse : 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 Dytiscidte, that we might define the family as 

 possessing posterior tibipe provided with elongate cilice ; but then many species 

 of Scarites in the Carabidre have the same parts quite as densely ciliate as have tha 

 Dytiscidse ; Avhile 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, w'e 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 ia the 

 Dytiscidse with that of a Trachypachys, or of other Carabidte, 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 ot the most marked 

 peculiarities of the family as a whole. 



III. — The Morphological Specific Chabacters. 

 THE FAMILY DYTISCID^.* 



The Dytiscidse are beetles, having the antennae eleven jointed, glabrous, and 

 shining, entirely destitute of exserted sette 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 maxillae 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 palj^iform, divided into two pieces by a transverse suture 

 in all the species except those of the genus Amphizoa. 



The presternum forming in the middle, behind, a process which jarojects 

 horizontally backwards, behind the front legs, towards the metasternum. 



The hind coxse 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. Tlie definition of the family should form a part of the fifth synthesis, but is placed here for the 

 convenience of those who have no knowledse as to what constitutes a member of the faniilv. 



