IS PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
starting from the ventral lateral portion of the anterior, right (actual 
right) margin of the seventh notum. As a sort of band it projects 
dowTiward (upward as specimen is held) and forward, bends trans- 
versely, passing beneath the ventral plate, and extends backward 
and upward toward a point opposite its origin. It does not reach the 
notum on this side, however, but is left 'floating' in the membrane. 
The lower, anterior corner of the notum, however, is prolonged down- 
ward toward but does not actually meet it, a narrow strip of membrane 
intervening. At its transverse bend this arch fuses with the fifth plate 
near its base, acting as a support. On the left side (actual left) a 
spiracle, or at least the vestige of one, is found within the chitin of the 
arch, while on the right side one lies in the membrane just anterior 
to the seventh notum. Logically these must be the spiracles of the 
sixth segment. I can therefore come to no other conclusion than that 
this arch is the vestige of that segment. This, of course, does not 
actually show that what is herein termed the 'fifth plate' and con- 
sidered to belong to the fifth segment may not possibly belong to the 
sixth. The supposition does not, however, seem unlikely, and is more 
reasonable than to suppose that the fifth sternum has been altogether 
lost. The fact that in a certain undescribed species of Sarcophaga 
the notum of the sixth segment may be found almost as completely 
developed as that of the seventh rather strengthens my opinion. 
Lowne ^ figures a similar condition in the blow -fly. In a species of 
\Yohlfartia found in the Rocky Mountains, I believe that absolute 
proof of my contention is presented. The fifth plate though ridged 
at the center is undivided and lamellae are lacking. It resembles the 
preceding sterna more than does the corresponding plate in any species 
of the three genera discussed in this paper, though the same condition 
is approached by a certain species of Sarcophaga. In this species the 
ventral arch of the sixth segment is covipleie, but at each side a line of 
division is apparent which may indicate the original marking off of the 
sternum or ventral plate. Normally this arch lies beneath and against 
the fifth ventral plate supporting it. But if the genital segments are 
pulled forth to the/?/// extent permitted by the connecting membrane, 
this ventral arch of the sixth segment is also pulled out, showing that 
it has not fused with the fifth sternum as in Ravinia, Sarcophaga, and 
Boettcheria. Also the membrane that connects it with that plate is 
' Lowne, B. T. The anatomy of the blow-fly, 1893-'95, vol. 2, pi. 50. 
