INTERLOCKING MECHANISMS IN COLEOPTERA. 



291 



2. By means of a groove on the dorsal face of the metathorax 

 into which the swollen inner edges of the elytra fit. 



3. By slipping the anterior edges of the elytra under the scutel- 

 lum and hooking them (a) on to the scutellum, or (/;) on to the 

 metathorax. Pressure derived from the retracted prothorax may 

 aid in keeping these edges in position. 



4. By hooking the anterior lateral edges of the elytra over 

 ridges or into grooves on the lateral faces of the metathorax. 



(a) Interlocking Mechanisms found in Lachnostcrna. 



LacJinosterna fusca is one of the lamellicorn beetles. The 

 head, prothorax and elytra show in dorsal view, together forming 

 a broad oval outline. The elytra almost cover the abdomen, 

 the exposed part being curved downward in such a way that it 

 cannot be seen from above. The abdomen is shortened and 

 rounded, and the elytra curve sharply downward at the sides and 

 posteriorly. 



The first three of the methods of interlocking mentioned above 

 are used in LacJinosterna. The hooking mechanism of the fourth 

 method is present, but is not functional. 



Fig. I. Mid-dorsal portion of the cross section of the elytra and metathorax of 

 Lachnostertia, showing the adaptation of the elytra to each other along the dorsal 

 suture and to the metathoracic groove. X 75- 



I. The method of joining along the dorsal suture is shown in 

 Fig. I, which represents a cross section of the mid-dorsal region of 

 the elytra. In this case the elytra are nearly as they would be 

 when the elytra were firmly closed, and are partially slipped into 



