THE CANADIAN ENTOMOLOGIST. 71 



connection with their arrangement and relative size, together with the 

 extent and form of the dilatation of the tarsi, furnishes excellent characters 

 for the separation of groups, and will be referred to again later. 



The larvae are aquatic and carnivorous, in form elongate, cylindrical 

 or fusiform, the head large and flat, the antenna; frontal, the mandibles 

 falcate, suctorial. The legs are terminated by two claws, and the abdo- 

 men lacks the tracheal branchiae seen in the Gyrinidce. They remain in 

 the water until full growth is attained, when they repair to some con- 

 venient place under a board, stone or tuft of vegetation, where probably 

 by the squirming motions of the body a cell is made in which the change 

 to pupa takes place; the length of time spent in this latter stage must 

 vary greatly in different broods and with the various species, but it was 

 found to be ten or eleven days in the case of Dytiscus verticalis, of which 

 a larva, taken at Bayfield, Wis., pupated on July i8th, the beetles appear- 

 ing on the 28th. 



T\\Q Dytiscid(z do not offer that diversity of form, colour and sculp- 

 ture presented by many of the families of terrestrial beetles, hence the selec- 

 tion of easily seen, though superficial, points on which groups might be set 

 apart has not been found practicable, and it has been considered wise 

 to use in the main the structural differences proved useful by such workers 

 as Drs. Sharp and Leconte in the primary divisions. Though the dis- 

 crimination of the genera and species will sometimes be difficult for the 

 beginner, it is hoped that at least in most cases a correct identification 

 will be the reward of careful work with sufficient material. The two great 

 divisions of the family, as defined by Dr. Sharp, are these: — 



,j I. Metathoracic episternum not reaching the middle 



coxal cavity (fig. 6a!) Dytisci fragmenlati. 



2. Metathoracic episternum reaching the middle coxal 



.^^,''V^^) '^'' cavity (fig. ']b) Dytisci complicati. 



Of the accompanying cuts, fig. 6 a represents a 

 diagram of a portion of the under surface of Lac- 

 cophilus, which belongs to the fragmentati, cc being 

 the middle coxal cavity. It will be seen that the 

 mesosternal epimeron {tns. epfu.) articulates at its 

 inner end with the metasternum {mi.), and thus cuts 

 off the metasternal episternum {i?it. eps) from the 

 "^' ^' coxal cavity. In fig. 7 b, however, which is a dia- 



gram of similar parts of Co/ymbites of the complicati, the mesosternal 



