igi4.] F. H. Oravely : An Account of the Oriental Passalidae. 183 



the angle at which the upper and anterior surfaces of the supra-orbital ridges meet is 

 moderate^ constant for each species, and is therefore of some taxonomic importance, 

 especially in the Aulacocyclinae. This angle may conveniently be referred to as the 

 apical angle of the ridge. In some species it is peaked, and in others always rounded • 

 but as the peak is very small and particularly liable to be rubbed away, this is not a 

 character on which very much reliance can be placed. In the genera Cylindrocaitlns 

 and Aurituhis this angle is developed into a conspicuous horn, which may be termed 

 the supra-orbital tubercle. 



The anterior end of the supra-orbital ridge is produced forwards in certain 

 species ; the process thus formed is as a rule relatively longer in small specimens 

 than in larger ones of the same species (compare fig. 20 with fig. 20b, and fig. 28 with 

 fig 28(0- The part of the anterior margin of the head from which this process is 

 developed may be called the anterioy angle of each side of the head. The size of this 

 angle is often of some taxonomic importance. From it a canthns extends outwards 

 and backwards, usually about half-way across the eye. This canthus may be either 

 rounded or truncate distally ; in the latter case the size of its external angle appears 

 to be of some slight taxonomic importance at least in the Aulacocyclinae. 



In the Aulacocyclinae, the posterior end of each supra-orbital ridge seems usually 

 to curve inwards and then forwards, towards the base of the central tubercle which 

 is present in all genera except Cylindrocaulus and Auritulus. This part of their 

 course is developed to a particularly striking extent in the genus Caidifer. Some- 

 times, however, even in the Aulacocyclinae, the inward prolongations of the posterior 

 ends of the supra-orbital ridges evihce a tendency to coalesce behind the central 

 tubercle. In the second section of the family the posterior ends of these ridges are 

 always united by what may be termed a supra-occipital ridge, except in the sub-family 

 Macrolininae in which this supra-occipital ridge extends outwards beyond them on 

 either side, curves forwards, and then disappears'. 



All the Passalids which come within the scope of the present paper, except 

 the genera Cylindrocaulus and Atiritulus, have a more or less prominent median 

 tubercle somewhere near the middle of the head. This is called the central tubercle. 

 It is as a rule more strongly developed in the Aulacocyclinae than in the remaining 

 sub-families, and assumes in the former a number of different shapes even the details 

 of which seem to be, as a rule, extremely constant in individual species or their local 

 races. In the second section of the family on the other hand, it is no more than a 

 longitudinal ridge more or less distinct and pointed in front, and such .structural 

 variations as it presents are usually small and not abso'utely constant, and are very 

 frequently obscured by friction. 



In the second section of the family a parietal ridge extends outwards on either 

 side of this central tuberdle. The angle between these ridges is as a rule moderately 

 constant in any one species, but is less constant than has sometimes been assumed. 



In the second section too, there is a pair of frontal ridges, which are never 



' In Ophrygonius singapurae the supra-occipital ridge unites the supra-orbital ridges, and is also con- 

 tinued outwards beyond them. 



