Memoirs of the Indian Museum. 



[Vol. VII, 



Thus two parts of the clypeus may be recognised, namely, a dorsal free part and a ventral 

 3>art closely opposed to the membrane uniting it to the labrum. The posterior part of the 

 free surface of the clypeus is sunk in the anterior margin of the frons, the two plates being, 

 however, separated by a well marked suture ; and the posterior angles are united with the 

 adjoining portions of the frons to form a pair of small tubercles. These tubercles are those 

 to which the name " outer tubercles " was given in my previous paper, a name which may 

 conveniently be retained for them. 



»« /: 



YlG. I. 



1. Oileoides subrecticornis (Kuwert). ") Anterior part of head. The outlines of the plates of the upper 



2. Chojidrocephalus granulifrons (Bates). > surface indicated by continuous, and those of the lower surface by 



3. Passalus affinis, Percheron. J dotted, lines. 



4. Passalus affinis, Percheron. Median section of upper and anterior parts of head. 



a.a. — anterior angles of head. 



an. — cavity for insertion of antenna. 



cl.f. — free surface of clypeus. 



cl.o. — opposed surface of clypeus. 



c.t. — central tubercle. 



fr. — frons. 



fr. r. — frontal ridge. 



f.v.s. — frontovertical suture. 



i.t. — inner tubercle. 



Ibr. — labrum. 



Ibr.m. — membrane between labrum and clypeus. 



o.t. — outer tubercle. 



s.or. — supraorbital ridge. 



v.t. — central tubercle. 



Having identified the clypeus in forms such as Oileoides subrecticornis, in which no doubt 

 with regard to it can arise, the fate of the free surface of this plate in other forms can readily 

 be followed. 



In species belonging to the subfamily Pseudacanthinae (of this paper) the clypeus is 



always separated from the frons by a definite suture, though this varies greatly in shape and 



in some species the inner tubercles are situated so as to interfere somewhat with its continuity. 



In the Proculinae, in a few species of Passalinae, and perhaps also in the Aulacocyclinae, the 



clypeus has the same structure as in the Pseudacanthinae, but the suture is absent. In all 



other species the free surface of the clypeus is reduced to (at most) a narrow transverse band, 



situated below the anterior margin of the head, and terminated laterally by a pair of small 



downwardly directed tubercles, the " ventral tubercles " of my previous paper (1914c, text 



fig. i, p. 181). These " ventral tubercles " — really the anterior angles of the reduced free 



surface of the clypeus — are extremely persistent, and their presence or absence almost always 



enables one to determine whether the anterior margin of the head really conceals this surface 



of the clypeus or includes it. To see them clearly, however, it is often necessary to remove 



the labrum. The outer tubercles are normally situated immediately above or a little to the 



outer side of them ; but in some forms these tubercles tend to come nearer together and may 



