2 GEO. H. HORN, M. D. 



In one species, pusillus, tlie males have at the base of the mandi- 

 bles a lobe prolonged over the labruni. PI. 1, fig. 16. 



The separation of the species, although much less difficult than 

 had been supposed, is not a thoroughly easy task, and the large 

 series before me, while rendering the attempt far more difficult than 

 it would have been with a few score of specimens, has made it pos- 

 sible to determine the limits of variation with greater certainty. 



The attempts at a monograph by Kiesen wetter were merely de- 

 scriptions of species based for the most part on small series, separated 

 without reference to structural characters. Color and sculpture af- 

 forded him the means of satisfactory separation, but with large series 

 these are shown to have but little value. 



In 1866, Schioedte attempted a division of the genus on charac- 

 ters drawn principally from the antennae ; Augyles, one of the sub- 

 divisions having but ten joints. The recognition has been shown by 

 deGozis to be extremely difficult and uncertain, and therefore of 

 doubtful value. In 1872, Mulsant and Rey proposed a means of 

 subdivision based on characters of far easier observation and giving 

 apparently more satisfactory results. 



It was observed by them that in certain species the elevated curved 

 line on the first ventral segment extended from the front angle by a 

 broad curve toward the middle of the posterior edge of the segment 

 and there terminated, while in others the line continued the curve 

 forward toward the inner edge of the coxa. In the former case the . 

 abdominal plates are called open (plaques abdominales ouvertes) and 

 in the latter entire (plaques abdominales enUhres). For the species 

 Avith entire plates the name Au gyles was erroneously adopted, which 

 deGozis has proposed to change to Littorhmts (Rev. Ent. 1885, p. 

 120). In our fauna but one species is known to belong here, au- 

 romicans. 



Recently Dr. Sharp* has observed a character of ccmsiderable 

 importance in its application to the grouping of the species. In 

 rather more than half our species there will be observed on the 

 metasternum an elevated line which begins at the middle of the 

 posterior border of the middle coxa, extending obliquely backward 

 joining the suture between the metasternum and its episternum. 

 That this has anything to do with stridulation as suggested by Dr. 

 Sharp seems to me extremely doubtful from its character as well as 



Biol. Cent. Am. vol. i, pt. 2, p. 116. 



