NORTH AMERICAN COLEOPTERA. 293 



in front, apex not eniarginate, base slightly arcuate ; prosternum 

 narrowly separating the coxse, slightly dilated behind them, the coxal 

 cavities open behind, angulate externally exposing the trochantin. 

 Elytra oval, usually convex, the humeri never prominent. Legs 

 moderately long, the posterior thighs stout, posterior tibiifi gradually 

 l)roader to tip, not sulcate on the outer edge, although slightly ex- 

 cavate near the tip. Tarsi of hind legs shorter than the tibia, the 

 first joint about one-third the length of the tibia and equal to the 

 other three ; claws simple. 



These insects are all of rather small size, many of them marked 

 with a yellowish white sinuous vitta on the elytra. The European 

 species are said to depredate on various species of Cruciferce ; the 

 .same is known of several of our s])ecies, but Prof Riley states that 

 the larva of P. vittata " feeds upon the roots below the ground (Third 

 Missouri Rep. p. 83)," the habit of those in Europe being to mine 

 the leaves. 



Our species, as well as those of Europe, may be arranged in two 

 parallel series. In the first, the fourth joint of the male antennte is 

 often thickened, the fifth always so, and at the same time elongate. 

 In the female the fifth joint is always longer than the fourth or sixth. 

 In the second series the antennae are alike in the sexes, the joints 

 2-10 not varying greatly in length. 



In the vast majority of our species the antenme are gradually 

 thicker to tip, but in pusilla, Lewisii and ceneicolUs, the antennae are 

 slender, as in Systena. 



The body is usually moderately convex, but several are quite de- 

 pressed, — (dbionica and pusilla. 



The males have the last ventral more or less impressed at ti}), 

 usually triangularly, but both the males and females of the first 

 series may be known from those of the second by the fifth joint of 

 the antenna) being longer than either of the adjacent joints. 



For this gen.us Crotch adopted the name Orchestris Kby., but the 

 reasons why it should not be followed have already been given by 

 Dr. LeConte (Proc Am. Philos. Soc. 1878, p. 615). 



Phyllotreta may be divided into two series in the following manner : 



Intermediate joints of niali' anteiiiUTe thickened and elongate, the fifth joint 

 always, sometimes also the fourth ; in the female the fifth joint is always 

 longer than either the fourth or sixth Series A. 



.\ntenii8e, not different in the sexes, the joints gradually slightly stouter from 

 the second to the tip, the fifth joint never longer than the sixtli-SERiES B. 



