4 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Only the posterior surface of the head shows any distinct division 
into sclerites ; those smaller ones immediately surrounding the occipital 
foramen are not considered. Radiating from the occipital region are 
five distinct sutures. From either side, at about the middle, a suture 
extends laterally and somewhat downward. These are the basal 
sutures of Lowne (PI. 1, fig. 6; PI. 2, fig. 11, bsu.). They do not extend 
to the oral margin as in the blow -fly, but end abruptly before making 
the downward bend, which may be verified by tracing the infolding 
of the chitin within the head along the line of the suture. Externally, 
there remains a distinct impression marking the course of its original 
continuation. Along this impression the vestiture of the cheeks and 
metacephalon (PI. 2, fig. 7) is separated by a narrow, but distinct, 
naked area. This external continuation of the suture is shown on 
the figure by a series of dashes. The area between the occipital region 
and the oral margin, which is enclosed by these sutures, is the meta- 
cephalon (PI. 1, fig. 6; PI. 2, fig. 11). From the dorsal part of the 
foramen three sutures extend upward, one from the center and one 
from either corner (PI. 2, fig. 11). The latter are the paracephalic 
sutures. Traced from within, the central one is seen to end about 
half way to the vertex. The area within the two outer or paracephalic 
sutures bounded below by the foramen and above by the vertex is the 
epicephalon (PI. 2, fig. 11, epc). Near its base on either side is a 
small, impressed, hairy spot as mentioned by Lowne on the blow-fly 
(PI. 2, fig. 7). Lowne, however, found on each side of the central 
suture, which he continued to the vertex, a triangular plate, which he 
termed the epi-occipital. Of these, I can find no trace though some 
specimens show a heavier chitinization in this region. By following 
the interior folds of the paracephalic sutures, these are found to extend 
upward to the dorsal, inner corners of the eyes and apparently end 
there. Careful examination, however, shows that they are continued 
onward and completely encircle the sockets of the eyes. This indicates 
then, that these sutures are only lines of junction between a single 
undivided portion of the head. Minus the epicephalon this is the 
paracephalon (Lowne) and includes all of the head except the meta- 
cephalon and the occipital sclerites. Its lateral halves are the para- 
cephala and bear the compound eyes and antennae. 
On the anterior surface of the paracephalon, a lower central por- 
tion is partially marked off by the frontal suture (PI. 1, fig. 1, fsu.). 
Through this suture, so called, the eversible frontal sac (PI. 1, fig. l,fs.) 
