NORTH AMERICAN ACROLOPHIDAE — ^HASBROUCK 505 



depending upon the species involved. However, their lengths may 

 always be obtained with reasonable accuracy. 



Several conditions may be established for those species exhibiting 

 elongate labial palpi: first, the segments never become progressively 

 shorter from the basal to the apical; second, the basal segment is 

 never demonstrably the longest of the three segments and typically 

 is somewhat to considerably shorter than the central segment; third, 

 when it is occasionally as long as or rarely longer than the central 

 segment, then it is always somewhat to considerably shorter than 

 the apical segment. Since the basal segment is quite large in all 

 species of Acrolophus, it is apparent from the above conditions that 

 those species having the unusually long palpi have attained them 

 through a relatively marked elongation of the central and apical 

 segments. 



Also, a variety of combinations of segmental lengths occur among 

 those species having elongate labial palpi. The basal segm.ent may 

 be much shorter than (mortipennellus) , about as long as (macrogaster 

 laminicornus) , or much longer than {dorsimaculus) the central 

 segment. Likewise, the basal segment may be much shorter than 

 (j)lumifrontellus), about as long as {jpropinquus) , or much longer than 

 (luriei) the apical segment. Further, the central segment may be 

 much shorter than (plumifrontellus) , about as long as (popeanellus) , 

 or much longer than (arizonellus) the apical segment. Intermediate 

 ratios occur among these major combinations, and the relative seg- 

 mental lengths may also vary slightly among the individuals of one 

 species. 



The denuded segments of the labial palpi are normally tubular or 

 cylindrical in form. However, in griseus griseus the central segment 

 becomes progressively laterally flattened distad, appearing very broad 

 in lateral aspect and very narrow in dorsal aspect, while the apical seg- 

 ment is even more markedly laterally flattened. In several species, 

 the apical portion of the apical segment is very slender and attenuated. 

 Those species having elongate palpi typically have setose compound 

 eyes, although griseus and dorsimaculus are two notable exceptions. 



In those species having labial palpi short or intermediate in length, 

 the vestiture obscures the segmentation less, and in some the segmental 

 lengths may be approximated without removing the scales. The basal 

 segment is again large, but it may or may not be closely appressed to 

 and recurved against the head. The central and apical segments may 

 be linear, subhnear, or somewhat curved. 



The short and intermediate types of labial palpi exhibit a simpler 

 and more consistent segmental condition than does the elongate type. 

 The segments invariably become progressively shorter from the basal 

 to the apical. Typically, the basal segment is considerably longer 



