274 BTNASTIN.E. 



densely hairy. Maudible entire, blunt at the end. Maxilla 

 terminating in a broad lobe, not tootlied ; palpus long. Mentum 

 short and tapering ; palpus very short. Prothorax with the front 

 angles acute and the hind angles rounded. Prosternal process 

 flattened, not erect, tufted at the end. Propygidium enlarged at 

 the expense of the pygidium, and its entire surface, except the 

 lateral angles, covered with microscopic regular transverse stridu- 

 lating ridges. Pygidium inturned beneath and very prominent 

 behind. Legs rather short and stout, the front tibia armed with 

 three or four strong teeth, and the middle and hind tibiae digitated 

 at the end ; tarsi of moderate length, the basal joint in the four 

 posterior legs distinctly triangular. 



cJ . The cephalic horn is generally longer than that of the female 

 and the pygidium is smooth and convex. 



9 . The pygidium is more or less conical. 



This is the first genus so far dealt with in which a stridulating 

 organ occurs. The delicate ridges occupy a considerable area, 

 ])ractically covering the penultimate dorsal segment, and the 

 vibrations are produced by movements of the abdomen causing a 

 sharp edge at the end of each elytron to be drawn across the ridges. 

 Darwin, in the ' Descent of Man,' called attention to a difference 

 of structure according to sex in the stridulating apparatus of 

 Oryctes, resulting as he supposed in its greater effectiveness in 

 the male. It is true, as he noticed, that the microscopic hairs 

 scattered over the propygidium are more numerous and con- 

 spicuous in the female, but the effective part of the striated 

 surface appears to be only a small area upon each side which is 

 bare in both sexes, and in the sculpturing of these areas I have 

 not been able to detect any such difference as described by 

 Darwin. It is strange that, although two of the species here 

 described are extremely common and well-known, I have failed to 

 obtain any account of the sound produced by them. 



Key to the Sjtecies. 



1 (2) Front tibioe 3-dentate : hind tibiae bluntly [p. 275, 



digitate nasicornis, L., 



2 (1) Front tibiaj 4-dentate : hind tibiae acutely 



digitate. [p. 276. 



3 (4) Elytra very smooth, minutely punctured .... desertortan, sp. u., 



4 (3) Elytra strongly punctured, the punctures 



annular. [p. 277. 



5 (6) Punctures of elytra small mulicauda, sp. n., 



6 (f)) Punctures of elytra large rhinoceros, L., 



[p. 278. 



