6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loi 



the upper surface of a single specimen, one short and inconspicuous 

 beneath the longer and often broader outer scale. In certain species, 

 such as squamosus LeConte and rhdbdotus., new species, the scales as 

 broad as long, and in squaTnosus with a suggestion of being bifid, as 

 in the genus Pachnephorus; in other cases truncate. Body beneath 

 usually less densely covered with finer scales especially on the meso- 

 sternum, metasternum, and abdomen, so that the surface shines 

 through, on the sides of the prosternum the scales thicker and like 

 those on the prothorax. Prosternum widely lobed below the eyes; 

 punctation of the breast and abdomen, on the first segment especially, 

 variable, from finely and sparsely punctate to coarsely, even rugosely 

 punctate. Tip of the abdomen in the male usually with a triangular 

 depression, in the female a deep rounded pit, though sometimes no 

 depression whatever {squamosus group), and in the male only a faint 

 one. Legs stout, not very long, shining, coarsely punctate with a 

 scale from each puncture, the posterior femora more or less distinctly 

 and bluntly toothed in most species; anterior tibiae usually with a 

 tooth on the inner side near the apex, and in the male a tooth at the 

 apex on the inner side of the tibiae of the anterior pairs of legs ; in 

 two species, the middle tibiae and, in the male, the posterior tibiae 

 with a spur before the apex; tibiae ridged and at apex dilated, the 

 claws appendiculate, not toothed. Aedeagus a typical eumolpid 

 structure in outer shape, being simply curved and with a somewhat 

 variably pointed tip, in the North American species not showing much 

 variation except in the squamosus group, in which the pointed tip is 

 exceedingly short and small, in the Central American and still more 

 in the South American species this organ often presenting considerable 

 differences in size and shape; in one group the tip broadly hollowed 

 out, as a scoop ; in a Trinidad species the aedeagus broad, heavy, and 

 truncate with a tiny tip in the middle, and in a Brazilian species the 

 tip drawn out into a long narrow point. 



The groups into which the species seem to fall naturally are here 

 arranged according to the external appearance coupled with the shape 

 of the aedeagus. The widely distributed Mississippi Valley species, 

 M. denticoUis (Say) , for instance, has close relatives in southern Texas 

 and Mexico {M. cyphus^ new species, and M. austrinus^ new species) 

 and farther south in southern Mexico and Central America {M. 

 carinatus Jacoby and M. melancholicus Jacoby), the last two being 

 larger and more coarsely punctate and in general more divergent in 

 outward appearance, but possessing an aedeagus that is of essentially 

 the same shape. The common species west of the Mississippi Valley 

 from Alberta to Texas, M. squamosus LeConte, has three close rela- 

 tives, M. intermedius, new species, M. severini, new species, and M. 

 pauxillus Schaeffer, the last found only in the area around Browns- 



