300 ROBERT S. BREED AND ELSIE F. BALL. 



(c) bitcrlocking MecJiaiiisiiis found in Tencbrio. 



The common meal beetle is one of the Tenebrionids. It may 

 be found abundantly through the summer months in granaries 

 and mills, or flying into houses. It is an elongated beetle whose 

 head, prothoracic and body regions are distinctly separated from 

 each other in dorsal view. 



The elytra of this beetle are not very firmly interlocked either 

 with the body or with each other. All four of the methods 

 previously mentioned are used in this interlocking. 



1. The mid-dorsal edges of the elytra are co-adapted much as 

 in Lachnosterna (cf. Fig. i). However minute teeth are found 

 along the dorsal surface of the ridge c, which fit in with similar 

 teeth on the ventral side of the ridge b. In three of the indi- 

 viduals examined the ridge on the right elytron fitted into a 

 groove on the left elytron while in two others the reverse was 

 true. 



2. The dorsal groove along the metathorax is both shallow 

 and narrow. Minute interlocking teeth are developed on the 

 thickened edges of the elytra and on the metathorax, as in 

 Thy mains (cf. Fig. lo). These teeth are more blunt than those 

 in TJiynialns and do not form as perfect an interlocking device. 



3. The inner anterior corners of the elytra slip under the 

 diagonal edges of the scutellum, showing very perfect co-adapta- 

 tion at this point. The prothorax does not fit tightly against the 

 elytra and is not used in holding them in place. 



4. The most interesting of these co-adaptations is that of the 

 lateral edges of the elytra with the episternum. As seen in Fig. 

 12, which represents the right lateral portion of a cross section 

 through this region viewed from behind, there are numerous 

 teeth on the inner surface of the elytron at s, which interlock 

 with teeth on the body wall at s' . Apparently the teeth at / and 

 /' do not interlock because: (i) long movable hairs are found 

 along the small ridge u, which would interfere with this action ; 

 (2) the shape of the body would prevent it ; (3) the teeth them- 

 selves do not seem stout enough to serve for this interlocking. 

 The action of the teeth at s and s\ working in connection with 

 the co-adaptations along the dorsal suture, would cause a strain 

 on the elytra which would hold them in place. 



