13 
racie, but Burmeister and later authors have given good reasons for 
considering it to represent the dorsal are of the prothorax or the pro- 
notnm, and it is so designated in this paper. 
Belonging to the mesothorax are the tegulae, anterior and lateral 
lobes of the mesoscutuin, mesoscutelluin, and lnesopostseiltellum (for 
brevity the second and third divisions are referred to as the anterior 
and lateral lobes and the scutelluin). The mesopostscutellum is found 
to enter very deeply into the interior of the thorax, doubtless to fur- 
nish attachments for the powerful wing muscles (fig. 3, i), and forms an 
invagination which nearly cuts the body in half at this point. The 
division of the body at this point is analogous to the separation in 
TZ 
Fig. 3. — Thorax of Pachynematus erichsonii: I, dorsal view ; II. ventral; III, lateral; and IV, lateral 
with segments separated. Prothorax: a, episternum; b, sternum; c, coxa; d, prohotum. Hemothorax: 
e, anterior, ami/, lateral lobes of scutum; r/, scutelluni; h, postscutellum ; i, mesophragma -.j, epimeron; 
A - , posterior plate of epimeron (?) ; I, coxa. Metathorax : m, scutum; n, scutelluin; o, epimeron ; p, 
coxa; t, tegula (original). 
Coleoptera between the j)rotliorax and mesothorax, the last thoracic 
division in sawflies being intimately joined with the abdomen, as are 
the last two divisions in beetles. Belonging to the metathorax are the 
metascutum and nieta scutelluin. 
This last sclerite — the* metascutellum— is commonly designated in 
descriptions as the " basal plates, 7 ' and these have always been mat- 
ters for dispute among entomologists. Of the Europeau writers, Andre, 
following Latreille and Audouin, considers them as constituting the 
dorsal arc of the first abdominal segment; Cameron, as representing 
a fourth thoracic segment (an impossibility from our accepted standard 
of the structure of insects), and West wood, on grounds which seem 
