2 U.S. NATIONAL MUSEUM BULLETIN 248 posthdmoos 



In certain species of the group, the preantennary portion of the head 

 (herein designated as the frons) is narrow and more or less bluntly conical, 

 with sides ranging from straight to more or less convex, while in others 

 this portion of the head may be flatly rounded to almost circular. 



The pleurites are usually not visible, but when clearly seen are found 

 to be almost entirely ventral. The tergites are always clearly defined, 

 continuous across abdomen, and always separated by a fairly wide hyaline 

 band. The outer ends of the sternites are sometimes visible, slighdy 

 separated from the pleurites, but only when the pleurites are clearly 

 defined, and then usually only in the posterior segments (IV to VIII). 

 Evidently the sternites are faintly pigmented, as a rule, and are concealed 

 by the more deeply colored tergites. 



In both sexes the chaetotaxy and structure of the distal abdominal 

 segment vary little between species — only in length and density of the 

 fringes of fine setae surrounding the anal opening in the female (see figures) . 

 Two figures of the male illustrate the chaetotaxy of this segment. 



The male genitalia (excepting those species from Phloeoceastes) follow more 

 or less the same pattern, especially the movable sclerite, but there are differ- 

 ences in various details, especially in the length of the basal plate and the 

 carinae of the endomeral sac. 



I wish to extend my appreciation to Miss Theresa Clay and Dr. K. C. 

 Emerson for the loan of certain species not found in my collection; with- 

 out them the present paper would not have been complete. 



All measurements are in millimeters; all drawings were prepared by 

 the author, and every effort has been made to secure their accuracy, 

 especially in the chaetotaxy. In many cases, setae which were lost in 

 the demounting or clearing are missing from the specimens, but their 

 alveoli usually have been located by high magnification and whenever 

 possible their approximate length given in proportion to related setae, 

 although there may be small errors in their estimated length. A few 

 species have never been cleared, and certain details are not distinctly 

 visible ; however, to preserve the specimens, it seemed best not to demount 

 them for cleaning. 



It is apparent that there is a very great similarity between certain 

 species, but it must be recognized that in the Menoponidae there are 

 rarely found the outstanding specific differences that are present so often 

 in the Philopteridae. Very careful study must be made of all the minute 

 differences, and it will be found that there may always be a sufficient 

 number of small differences to warrant nomenclatural recognition, at 

 least subspecifically. 



KEY TO SPECIES OF MENACANTHUS PARASITIC ON PICIDAE 



1. Sternal head spines very short, scarely longer than their width at 



base 2 



Sternal head spines at least twice as long as width at base .... 4 



