150 PROCEEDINGS OF THE ACADEMY OF 



metathoracic spines long, prominent, obtuse; areolet narrow, 

 closed ; abdomen smooth and polished. Length i^ lines. 

 Orizaba. 



Subgenus Mesostenus. 



In this subgenus the form is much more robust than in Poly- 

 cyrtiis. The head has no frontal spine or tubercle; the lobes of 

 mesothorax generally not prominent, often scarcely indicated ; 

 the metathorax varies in form, with the spines sometimes long and 

 acute, and sometimes entirely wanting ; the areolet of anterior 

 wing, always small, also varies much in shape, and although gene- 

 rally closed, is sometimes open. 



The species are numerous and ma}' be separated by the cha- 

 racters a;iveu in the following table. 



Abdomen black, banded with white or yellow : 

 Mesothorax with white discal spot : 

 Metathorax with lateral tubercle or spine : 



Metathorax with three black stripes, connected by a broad black band 

 at base ; posterior coxfe pale fulvous, their femora black within ; 

 scntellum white at apex 1. aztecus. 



Metathorax as in aztecus ; posterior coxoe with broad black lateral 

 stripe, their femora black above and within ; scutelhun white at 

 apex 2. propmquus. 



Metathorax with three black stripes, connected at base by a narrow 

 black band ; posterior coxre with a narrow black stripe, tlicir 

 femora black above and beneath ; second abdominal segment with 

 a transverse whitish mark on basal middle ; scutellum white at tip. 



3. compactus. 



Metathorax black, with two elongate white spots covering spines, 

 and a large white spot on each flank ; posterior coxa; with a sub- 

 cordate black mark above, their femora trivittate with black ; scu- 

 tellum white 4. discus. 



Metathorax as in discus ; posterior coxre with two short black stripes 

 above ; their femora bivittate with black ; scutellum white. 



5. facilis. 



Metathorax black, tubercles and spot on each flank, Avhite ; posterior 

 coxfc marked Avith black, their femora black beneath and at tips ; 

 scutellum white 6. acceptus. 



Metathorax black at base, with three slender black stripes ; posterior 

 coxa; with lateral black stripe, their femora entirely pale fulvous ; 

 second abd(nninal segment broadl}' Avhite at base and apex ; scu- 

 tellum white 7. modicus. 



Metathorax fulvous, black at base above ; discal spot of mesothorax 

 often furcate anteriorly ; legs, except tips of tarsi, fulvous ; scu- 

 tellum white 8. communis. 



