OF WASHINGTON, 103 



present an epimerum (Epm), an episternum (Eps), a pleural 

 suture (PS), a pleural ridge internally (PR) under the suture 

 between the epimerum and episternum, a wing process {WP), 

 and usually a rudimentary parapterum (figs. i6 and 17, P) 

 though sometimes a well-developed one (fig. 23, P). The 

 coxal process is absent in the metathorax but is usually present 

 though small in the prothorax and mesothorax. 



The writer has not had the opportunity of making an ex- 

 haustive study of the trochantin in the Coleoptera, but in all 

 forms examined it was found only in the prothorax and meso- 

 thorax, and in both of the latter is sometimes fused with the 

 coxa. In the Silphidae and Buprestidae it is well developed as 

 a distinct and exposed plate intermediating between the epi- 

 sternum and the coxa, and in these families, especially in the 

 Silphidse, has a distinctly orthopteran appearance. It is gener- 

 ally, however, much smaller and concealed within the coxal 

 cavity as a small plate articulated to the head of the coxa in 

 front of the articulation of the latter to the coxal process, and, 

 moreover, in some cases it appears to take part in the formation 

 of the socket receiving this process. It is thus in Carabidse, 

 Dytiscidae, Cerambycidae, and Scolytidse. 



There may be some question as to whether this sclerite is the 

 homologue of the trochantin of the Orthoptera and the Eu- 

 plexoptera. However, it is the plate originally named tro- 

 chantin by Audouin, for he describes it specifically only in 

 connection with Buprestis gigas. He states, however, that it 

 lies between the coxa and the epimerum, but, undoubtedly, he 

 regarded the posterior one of the several divisions of the epi- 

 sternum in Buprestis as a part of the epimerum. 



The metathorax usually dififers much in both its notal and 

 pleural parts from the mesothorax. The metanotum is a large 

 plate of definite and constant shape in all beetles. Calosonia 

 scrutator (figs. 24 and 25) afifords a typical example. There 

 are apparent sutures on the dorsal surface but they are in all 

 cases the external marks of ridges on the ventral surface 

 (compare figs. 24 and 25, /, n, p). The anterior margin bears 

 a phragma and the posterior is thickened into a small mar- 

 ginal ridge (/) which bears the axillary cords at its ends {Ax). 

 A median dorsal groove is present though frequently inter- 

 rupted by a membranous area. The same articular processes 

 for the wing sclerites are present on each side as in the 

 Orthoptera. 



The most important point to notice on the back of the 

 coleopteran metathorax is the pseudonotum (Pn), a plate lying 

 behind the true notum, carrying a phragma ventrally, and 



