416 



DK. F. LEUTHIsEE ON THE ODONTOLABIISI. 



order to facilitate their study, we will divide them into three sections, and begin with 

 the second. The diiferent male forms are arranged on PL XCV. so as to admit of 

 easy comparison. 



A. 



B. 



Mcntum hairy. 



0. seratus. 



0. carinatus, Li\ 



0. castelnaudi.- 

 0. sommeri. 



-a 



a I I 



1^ 1^ 0. lowii. 



5 .- <; 0. brookeanus. 



c. 



Mentura hairless. 

 — 0. latipennis. 



0. fratellua. 



The females of this section (PI. XCV. figs. 5, 10, 1(3) agree in appearance and colour 

 with those of the two preceding groups. The coloration reminds us of 0. cuvera and 

 0. icoUastoiii, in 0. sommeri (Hgs. 10,11); in the variety (fig. 12) the yellow colour 

 already extends to the sides of the prothorax, and is still more variable in 0. brookeanus 

 (figs. 16, 17, 18). In 0. castebmudi, which is nearly twice as large, the elytra are 

 almost entirely yellow, owing to the disappearance of the triangular spot, the last 

 remains of which are seen in a small stripe at the base and another on the suture 

 (fig. 5). 



In the males the black triangular spot on the elytra is reduced to a narrow black 

 line on the suture, and the pale coloration extends to the sides of the prothorax, and 

 even to the head and to the under-surface of the body. Apart from the immediately 

 obvious similarity of the males, they present the following morphological resemblances, 

 viz. : a large broad head, a short and very broad prothorax, long curved fore legs, with 

 few spines, and in the telodont forms, a broad quadrangular epistoma-like clypeus. A 

 character peculiar to all the species of this group is the hairy mentum, and in the 

 three last species the gula is also hairy. Notwithstanding the diflerence of the man- 

 dibles in the telodont forms (figs. 1, 13) (which are at present insufficiently known in all 

 the species) they are remarkably similar, both in the priodont (figs. 8, 15), amphiodont 

 (figs. 4, 7, 9, 14), and mesodont (figs. 2, 3, 6). This resemblance can only be accounted 

 for by a common origin and hereditary descent, with a tendency to modification — a view 

 which is likewise confirmed by their geographical distribution, for 0. sommeri occurs 

 in Banka (and Sumatra), and is intermediate between 0. castelnaitdl and 0. Irookeanus, 

 which occur in Sumatra and Borneo, between which islands Banka is situated ; and 

 0. lowii, which is most nearly related to 0. hrookeanus, likewise occurs in Borneo. 



The amphiodont form of 0. castelnaudi (PI. XCV. fig. 4) easily leads us on to the 

 male form of 0. lati])ennis (PI. XCVI. fig. 1) belonging to Section C. The shape of 



