16 PROC. ENT. SOC. WASH., VOL. 24, NO. 1, JAN., 1922 



The size of the third antennal joint as compared with that of 

 the second and fourth is a character which has been used by 

 nearly every worker with the genus; in spite of the fact that 

 there are some intermediate and variable species, lack of more 

 satisfactory characters has made necessary its continued use. 

 The sexes can be distinguished by the presence of a thick and 

 erect pubescence on the inferior margin of the fourth to eleventh 

 antennal segments of the male (fig. 12). In some species this 

 pubescence is very short and therefore difficult to see (e. g. 

 cribricollis Candeze) but so far as the writer knows the character 

 can be seen in all the American species. 



PROTHORAX. Throughout the genus the notum (fig. 13) 

 is roughly quadrilateral, but the outline of the lateral margins 

 is so variable within a species that this character has proved 

 less valuable than many earlier writers have supposed. The 

 anterior margin of the notum may be truncate or sinuate; the 

 anterior angles are sometimes produced and sometimes extend 

 no further anteriorly than the middle of the margin itself. 

 Posteriorly the notum of the prothorax is nearly truncate, 

 varied by slight sinuations. The posterior angles are generally 

 prominent, though varying in width and length with the species. 

 Medianly from each posterior angle, at a distance varying with 

 the species, is the short sulcus (sul, figs. 13 and 15) which varies 

 somewhat in length, width and direction; it is apparently of 

 slight taxonomic value. Another character sometimes, but 

 not often, useful is the presence or absence of a median basal 

 groove on the notum (shown in fig. 13) 



The posterior angle always bears one carina and in some 

 species a second, more or less well-defined, which diverges 

 inwardly. Candeze and other writers have attached much 

 importance to um- and bicarination, much more in the present 

 writer's opinion than the character merits, for in many species 

 a series of specimens will show all gradations from a well-defined 

 second carina to the most vague and uncertain suggestion of 

 bicarination; this is particularly true of decumanus Er. The 

 first carina is variable in length, and the second, when present, 

 is always the shorter. 



The notal punctuation is variable, but is generally (except in 

 opacicollis Leconte and gradatus Leconte) noticeably sparser 

 and finer on the disc than on the rest of the notum. 



The relative length and width of the notum have been very 

 generally used in the taxonomy of the genus, but unfortunately, 

 writers have differed in their use of these measurements, with 

 the result that much confusion has arisen. The present writer 

 has found it convenient to confine himself (as Candeze usually 

 does) to the use of the median measurements ', as indicated in the 

 figure of M. communis Gyll. (ML and MW, fig. 13). Through- 

 out the genus the relative width of the prothorax is greater in 

 the female than in the male. 



