1918.] F. H. Gravely : Passalidae of the World. 97 



and more crescentic scars on the mentum. The outer tubercles of the head are practically 

 symmetrical, the right one being slightly broader than the left, at least in the Tondano 

 specimen. In this specimen the space between the inner and outer tubercles is surrounded 

 by fine but distinct ridges, of which the lateral and posterior are straight, and the anterior 

 procurved. In the large specimen the lateral ridges are absent, the anterior one is 

 procurved and the posterior one recurved ; and in the Menado specimen even the anterior 

 and posterior ridges are indistinct. 



Plesthenus quadricornis, Kaup. 

 PI. I. 



Eriocnemis quadricornis, Kaup, 1868a, p. 26. 

 Plesthenus quadricornis, 1871, p. 40, pi. iv, fig. 4. 



Four specimens of the northern race, quadricornis, s. str. [(see above, p. 96), from 

 Toli-Toli and three from Menado, both in Northern Celebes. One specimen of the southern 

 race, gelon (Schaufuss, 1885, pp. 187-188), from Samanga, one from Patunuang, and two 

 from Macassar, a 1 in Southern Celebes. Length of the northern race 49-53 mm. Length 

 of the southern race 55-60 mm. 



P. quadricornis differs from P. invitus only in having the right outer tubercle 

 somewhat longer, and sometimes more obliquely truncate or even acuminate, and in having 

 the left outer tubercle smaller and acuminate or obsolete. In the Toli-Toli specimens 

 the left outer tubercle is an acutely pointed process, scarcely shorter than the inner side of 

 the somewhat obliquely truncate right outer tubercle. In the Menado specimens it is much 

 shorter, the apex being rectangular or even obtuse. This is the case in the specimens from 

 Samanga and Patunuang also ; but in these the right outer tubercle is somewhat slenderer 

 and more obliquely truncate ; in size, moreover, these specimens resemble those from 

 Macassar and not the preceding. In the Macassar specimens the left outer tubercle is- 

 scarcely recognizable, and the right outer tubercle is acuminate. 



The two above described species of Plesthenus may be identified thus : — 



r The outer tubercles approximately symmetrical, both of them 



truncate . . . . . . . . . . P. invitus, p. 96. 



The outer tubercles asymmetrical, the right one much larger 

 than the left and truncate, except when the latter is obsolete, 

 in which case it may be acuminate ; the left one never 

 truncate . . . . . . . . . . P. quadricornis, p. 97. 



Genus MASTOCHILUS, Kaup, 1868a, pp. 19-20, corrected 18686, p. 31. 



Type, Passalus polyphyllus, MacLeay, 1826, p. 439. 



This genus, as pointed out above (p. 77), may be divided into four more or less distinct 

 sub-genera : — 



The mentum laterally with a narrow depressed matt border, or 

 more extensively matt ; large Australian forms with very 

 1 -/ short antennal lamellae ; always symmetrical ..' .. Pharochilus, 1 p. 98. 



The mentum uniformly glossy in fresh specimens ; the antennal 



lamellae much longer ; or not Australian . . . . . . . . 2. 



1 Kaup, 1868«, pp. 20-21. Type, Passalus dilatatus, Dalman. 



