36 NORTH AMERICAN 



Transverse carinae of abdomen tricuspid a. 



Transverse carinae 4-cuspid b. 



Transverse carinae not cusped c. 



Subgroup «. 



In this subgroup I have employed several subsidiary characters, 

 depending upon the form of body and sexual modification of the male 

 in order to form four sections as follows : — 



§ 

 Form extremely slender, nearly cylindrical ; elytra much shorter than the 

 prothorax ; head much wider than the elytra ; length 3.1-3.4 mm. 



20. straiigulatiis. 



§§ 

 Form very slender, conspicuously depressed ; sides nearly parallel ; abdomen 

 fully as wide as the contiguous elytra ; segments decreasing extremely 

 slowly in width, and usually strongly extended after death; length 

 2.8-3.7 mm.* 

 Prothorax widest distinctly before the middle. 



Elytral suture and pronotum nearly equal in length. 



Form excessively slender ; elytral punctures coarse and rather distant. 



21. tenuis. 

 Form slightly more robust ; elytral punctures finer and closely 



crowded 22. anglistus. 



Elytral suture much longer than the pronotum. 



Sixth ventral segment % deeply and rather narrowly sinuate poste- 

 riorly 23. (1 iliac ilis. 



Sinus of sixth segment % extremely broad and feeble. ..24. Pettiti. 

 Prothorax widest at or slightly behind the middle 25. SCrilpeilS. 



§§§ 

 Male having the lateral borders of the impressed area of the fifth ventral seg- 

 ment, in the form of ridges which terminate posteriorly in acute teeth. 

 Large species. Length 3.7-4.8 mm. 



* The insects in this small section increase gradually in robustness in the 

 order given from tenuis, which is very slender and more filiform than any 

 other within our territory, to scrupcus which, although elongated, is slightly 

 more robust than two or three of the next section, as, for instance, subtiliS, 

 indigens, and ingratus; it will therefore be merely safer, if the species be a 

 slender one, to first consult this table and its accompanying descriptions 

 before proceeding to the larger table following. The section is retained dis- 

 tinct because of the depressed appearance as well as the slender form of the 

 species comprised within its limits. The protrusion of the abdomen may 

 result from the manner in which the insects are killed; if in alcohol the 

 abdomen is generally protruded. I can only state that in all the specimens 

 before me the abdomen is extended, and do not pretend to assert that this is 

 a physiological peculiarity. 



