NORTH AMERICAN COLKOPTERA. 3 



angular, becomes exceptionally oval. The prosternal lobe is usually 

 prominent and strongly rounded, tiie posterior process extending 

 behind the coxse is subject to considerable variation which has been 

 largely made use of in the following tables ; when fully developed 

 the process is nearly horizontal beneath, or feebly curved upward 

 with marginal impressed lines between the coxse, extending forward 

 and curving round the coxal cavities and backward to, and meeting 

 at, the apex. The lines frequently disappear immediately behiiul 

 the coxte and the process itself may be strongly ascending beneath 

 and abbreviated in length. The submarginal sutures of the pro- 

 thorax normally reach from the basal angle to the anterior third or 

 fourth, but in some species they are quite variable, so that their 

 length does not aftbrd any distinguishing character. I have, how- 

 ever, laid some stress upon their development in one or two instances. 

 The mesosternal fossa presents no particular feature worthy of re- 

 mark, exce()t the one used in the second table to separate convexus 

 and its allies. This difference is very obvious in these species, sepa- 

 rating them from all the others. The hind coxal plates vary greatly, 

 and while of much importance in the first division, in the second 

 very little use can be made of them, one important exception, how- 

 ever, occurs in the case of dispar, which seems almost worthv of 

 being placed as another genus. Reference is made in the present 

 paper to three other forms. In the first the plates are narrowed ex- 

 ternally, the hind margin extending from the trochanter obliquely 

 forward; in the second the hind margin is transverse; in the third 

 the plates are dilated, that is, extending outward and obliquely back- 

 ward from the trochanter. The variations in the tarsi are treated in 

 the descriptions following. The claws, while showing some sliaht 

 dittl^rences in size, are, on the whole, very much alike. 



The sexes frequently differ in size, the variation between the 

 smallest males and the largest females being sometimes very great, 

 and in studying the species it is very desirable that due attention be 

 given to the sexes of the specimens under consideration. 



If any apology is needed for the length of the descriptions given 

 I can only plead the insufficiency of many previous ones and the 

 desire to leave as little as possible for gi-anted. 



I am greatly indebted to Dr. Horn for suggestions and encourage- 

 ment as well as for the loan of specimens. To the Cambridge i\Iu- 

 seum, to Mr. Ulke and others, I would express my acknowledgements 

 for favors received. 



