BY THE REV. T. BLACKBURN. 139 



they may be identified with some ease and confidence has proved 

 no easy one. I think, however, that I have succeeded in speci- 

 fying characters which will at least prevent the confusion inter se 

 of any of those dealt with in this memoir ; but in order to do so 

 I have had to avail myself of characters that require some 

 preliminary observations. 



I find that not a few species of Heteronyx are distinguished 

 from their nearest allies by little that is tangible except differ- 

 ences in puncturation, and in the relations to each other of the 

 labrum and clypeus. Though these distinctions are abundantly 

 satisfactory as separating the species, they are nevertheless 

 of degree and difficult to render available to the reader of a 

 memoir. The former of them I attempt to indicate (as regards 

 the prothorax) by specifying that " closely " punctulate means in 

 the tabulation having the punctures so placed that twenty or more 

 might run down the middle of the disc if they were placed in a 

 longitudinal line and at about what is actually their average 

 distance one from another. The relation of the labrum to the 

 clypeus («.e., the extent transverse and vertical of the portion of 

 the former overtopping the plane of the latter, and the convexity 

 of the curve of the former) seems to be a very important and 

 reliable character for distinguishing one species from another, but 

 it is extremely difficult to express in definite terms. After much 

 consideration I have adopted a method of expression that I now 

 proceed to explain. If a specimen of Heteronyx belonging to this 

 section be viewed from above it will be found that there is a 

 certain point of view (a point perpendicularly above the suture of 

 the elytra, from which the eye looks more or less obliquely forward 

 along the surface of the insect) whence the outline of the front 

 of the head, from eye to eye, appears as a continuous trisinuate 

 or trilobed curve. The nature of this curve depends entirely upon 

 the relation of the labrum to the clypeus, and therefore seems 

 fitted to serve as an index of that relation ; I find it very constant 

 in individuals of the same species. In the following descriptions 

 this curve when spoken of is called the " trilobed outline " of the 

 head. In species whose clypeus is deeply and widely emarginate, 



