OF WASHINGTON. '!') 



(lateral) pair of plates, then is pushed through this opening and 

 the egg (or the eggs) is thus inserted into the slit. 



It is well known that the images of Plateumaris differ in habit 

 from those of Donacia : the former occur on palustral plants and 

 the latter on truly aquatic plants. The supposed oviposition in 

 Plateumaris greatly differs from that of the true Donacia, so far 

 as the life-histories of these are known, and would seem to indi 

 cate a corresponding difference in the habits of the larva. 



I am not aware that any similar structure of the ovipositor has 

 been observed in other Coleoptera,* and while in several families 

 (especially Cerambycidas) the eggs are inserted into the tissues 

 of plants, the ovipositor is at most a piercing instrument, but 

 never a saw. 



From an examination of a number of females of Plateumaris 

 it can be readily seen that the form of the ovipositor, and more 

 especially that of the ventral plate, offers excellent characters 

 for the distinction of the species. The material at present at my 

 disposal is, however, by no means complete enough to enable me 

 to give a synoptic table of the species based upon this character, 

 and I confine myself to indicate briefly the various types of this 

 structure in the North American species : 



a h 



Fig. i. Outer ventral plate of the ovipositor in Donacia (subgenus Plateumaris): 

 a, Donacia, n. sp.V; l>, D. rufa; c, D . etua.rgina.ta. 



ist Type. Ventral plate with a prominent, acute tooth on each 

 side of the junction of the parallel basal part with the apical part ; 

 the latter triangular with the sides straight and finely serrulate ; 

 terminal point long and slender, spine-like. 



This type occurs only in D. rufa. 



2d Type. Ventral plate without such tooth ; apical part more 

 or less triangular, with the sides either straight or arcuate, edge 

 finely serrulate ; terminal point acute but not spine-like. 



Most of our species belong here; specific differences are indi 

 cated by the greater or smaller width of the plate, the longer or 



* The pupae of the Chrysomelid genus Sagra have been found within 

 the steins of plants, but \ had no opportunity of examining female speci 

 mens of this genus. 



