2^70 Trans. Acad. Set. of St. Louis. 



tures of the fifth and sixth tergites modified into coarse and 

 elevated, subelongate asperities, usually with one more distinct 

 at the centre, and in some cases as in bakeri and laxicornis, 

 another at each side more apical on the fifth tergite, and the 

 sixth sinuate at tip, with porrect asperities, each bearing a 

 short stiff bristle, about the contour of the sinus, the female 

 having the punctures throughout minute and but feebly as- 

 perulate, with the sixth tergite simple at the apical margin 

 and sinuato-truncate. In nigrina the central tubercle of the 

 fifth tergite is very small and slightly elongate, those more 

 posterior being scarcely distinct and in hrevicornis it is similar, 

 but in the former the sinus of the sixth tergite is coarsely 

 serrulate, while in the latter the serrulations are extremely 

 minute and sparser. In minor the central tubercle is very 

 minute and scarcely elongate. In californica the median 

 tubercle is before the centre and scarcely larger than several 

 of the others. There is but little diversity in these sexual 

 characters, so that it is scarcely necessary to describe them in 

 each instance. 



Silusida n. gen. 



This genus is represented thus far by two species, one at 

 least very abundant in individuals, both small in size and of 

 rather dull lustre. They resemble Venusa in general form, but 

 may be distinguished at once by the short, strongly and 

 gradually incrassate antennae and by the feebly rounded sides 

 of the prothorax toward base, with less distinct basal angles ; 

 they may be described as follows : — 



Form rather stout, somewhat depressed, parallel, feebly shining, the pubes- 

 cence pale, very short but abundant and distinct, pale flavo- testaceous 

 in color, the head, median parts of the prothorax, elytra toward the 

 external apical angles, except along the apex, and abdomen from about 

 basal third to the middle of the fifth segment, blackish; legs pale, the 

 antennae slightly dusky; head and prothorax very minutely and obso- 

 letely reticulate, the former small, transverse, with rather large promi- 

 nent eyes, minutely, sparsely punctulate, the antennae scarcely longer 

 than the head and prothorax, rapidly and strongly incrassate, the sec- 

 ond joint much longer than the third, both slender and elongate, four 

 to ten very strongly transverse, greatly increasing in width and per- 

 foliate; prothorax fully three -fourths wider than long, very much wider 



