54 



the apical internal spine. The external edge of the '• apical 

 plate" runs backward (i e., up the tibia) for a length varying 

 with the species as a smooth ridge and then becomes serrated, 

 each serration bearing a long seta. This ridge I shall call the 

 "inferior ridge." From the anterior external corner of the 

 "apical plate" there rises a line, which can be traced as a 

 distinct rib or ridge along the following course, viz., around 

 the whole contour of the under surface of the two large apical 

 external spines of the tibia, and then backwards (i.e., up the 

 tibia), at first forming the external margin of the tibia and 

 then (higher up) passing to the under side until it joins the 

 " inferior ridge " of the tibia at a variable distance (but never 

 very far) from the apex of the femur. The portion of this 

 ridge above the two large apical spines, like the " inferior 

 ridge," is cut into a series of denticulations, of which those on 

 the part where it forms the external edge of the tibia are, if 

 they are present at all, pointed outwards, while those on the 

 portion that is underneath the tibia are pointed downwards. 

 Each of the denticulations of this " exterior ridge " (as I shall 

 call it) bears a long stiff seta. 



I was led to make this exact observation of the structural 

 characters in the front tibia of Carenum by experiencing the 

 unsatisfactory nature of the expressions " bidentate " and 

 " tridentate " as applied to the external margin of those limbs. 

 I found, for example, that two specimens of the same insect 

 might appear to oscillate between being "bi" or "tri" dentate 

 in that respect, according to the position in which the anterior 

 legs were set ; and further, comparing (7. Icsvigatum, Macl., and 

 C. Odewalini, Cast, (placed by Mr. Macleay in different genera 

 mainly on this character), I failed to discover any difference 

 in the dentation of their anterior tibiae. 



As far as I have been able to examine the species of Carenum 

 I find that the "exterior ridge" in them all possesses either 

 three or four distinct denticulations in the upper portion {i.e.., 

 the portion above the two large apical teeth), and that the size 

 and position o£ the denticulations varies considerably, but is 

 tolerably constant in examples of the same species. In some 

 species they are larger than in others ; in some the lowest or 

 the lowest two are a good deal directed outwards (because the 

 exterior ridge limits the tibia externally for a certain distance 

 before passing to the under surface), so as to be partially 

 visible when viewed from directly above, but in all that I have 

 examined there are at least three teeth to be seen above the 

 apical two if the tibia be viewed from a point a little outside 

 that from which it would be looked down upon perpendicularly. 

 Thus the distinctions founded on the dentation of the " exterior 

 ridge " are for the most part distinctions of degree, and by no 



