INTERLOCKING MECHANISMS IN COLEOPTERA. 



293 



about one millimeter back of the scutellum. Figs. 5 and 6 show 

 cross sections of the elytra from near the middle region. In all 

 ot the specimens examined, the ridge on the left elytron hooks 

 into the groove on the right elytron. 



Fig. 4. Similar to Fig. 3. Right elytron. 



75- 



2. Figs. I to 6 show the thickenings of the lower face of 

 each elytron along the mid-dorsal edge in cross section. Figs, i 

 and 2 show the form of these thickenings in the metathoracic 

 region. Beneath these thickenings there is a groove along the 

 metathorax, well stiffened with chitin, into which the thickenings' 

 fit tightly when they are interlocked. This groove is seen in 

 cross section at g, in Fig. i. The thickenings of the elytra in the 



Fig. 5. Cross section of the mid-dorsal thickening of the left elytron of Lack- 

 nosterna as seen near the posterior end of the elytron. X 75- 



anterior part of the suture are more abrupt than elsewhere, the 

 contour of the under side of the elytron being here S-shaped in 

 cross section (Figs. 3 and 4), so that the thickenings hook into 

 the metathoracic groove, which is slightly wider in its ventral 

 than in its dorsal part. 



