322 MEMOIRS ON THE COLEOPTERA 



disappears within the abdomen. This is the most perfect arrange- 

 ment for maintaining an unbreakable hold during copulation; the 

 penis proper is then protruded between the reversely hooked plates. 



Polyphylla Harris. 



The species of this genus are rather sparingly diffused throughout 

 the northern hemisphere, but are especially abundant in the 

 western parts of the nearctic regions. There is considerable diver- 

 sification in habitus but not so much in structural features of an 

 essentially generic nature, and the name Macronoxia, proposed for 

 certain species by Crotch, probably cannot be maintained. The 

 sexes differ in appearance far less here than in Thyce; the disposition 

 of the vestiture is virtually the same in male and female and the 

 sexual marks are found principally in the structure of the antennae, 

 anterior tibiae and clypeus, the antennal club being very long, 

 distally recurved and y-lamellate in the male and small, straight 

 and with five full and one or two partially developed joints in the 

 female. The pronotal punctures are sometimes rather coarser and 

 sparser in the female than in the male, but this is by no means a 

 general rule. The tibial modifications are analogous to those 

 affecting the genus Thyce. The female in some species, especially 

 in those having tridentate anterior male tibiae, are extremely rare, 

 and among all the numerous individuals in this group at hand, there 

 is only a single example of that sex; in the lo-lineata section how- 

 ever, females frequently occur, but in the Atlantic coast variolosa, 

 among my 28 individuals there is not a single female. There is 

 sometimes a singular variability within specific limits in the form 

 of the squamules, especially of the pronotum; in lo-lineata, for 

 example, the scattered squamules are generally scale-like, but in 

 two individuals before me they become finer and hair-like, without 

 other apparent distinguishing features. 



The various forms that must be recognized taxonomically are 

 extremely numerous in the western and Sonoran faunas of North 

 America, and it becomes a problem to know how to treat them. 

 To consider them all as species would be inadvisable in the present 

 state of opinion in regard to the meaning of the word species, and I 

 have therefore placed many of them in the category of subspecies, 

 although, if a detailed study of the genitalia were to be made, such 



