44 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
southern species in which the dusting of the first segment is yellowish 
or golden. Differences in shape exhibited are very useful but hard to 
define. In Ravinia it is practically constant for all species; several 
forms occur in Sarcophaga. When the anterior and posterior surfaces 
are parallel, that is, the latter is flattened (see figure of S. haemorrhoi- 
(lalis ]\Ieigen), the appearance in profile reminds one of half of a 
spherical segment and an additional idea is given by stating whether 
the anterior and posterior surfaces are equal or one larger or smaller 
than the other. In S. tuberosa sarraccniae (Riley) the profile outline 
extends as a curve from the back of the first segment to the base of 
the forceps, and suggests a portion of a round object, — such segments 
are rotund. The outline may not extend as a curve cjuite to the 
forceps base, the posterior surface being slightly flattened. In one 
American Sarcophaga the second segment is much smaller than the 
first ; it is quite shallow, the posterior and dorsal surfaces represented 
by a continuous curve without any line of demarcation between them, 
and the whole resembles a disc, — such forms as this are called dis- 
coid al rather than rotund and may be either conical or flattened. 
Various modifications of the above term are used for descriptive 
purposes (see section on external anatomy for definition of the various 
surfaces of the second genital segment). In species showing a dis- 
coidal character of the second genital segment the "progenital" 
tergum projects well forward into the cavity of the first segment and 
often carries the penis forward -with it. The size of the second seg- 
ment as compared to that of the first is not so important as other 
characters, being more or less dependent on them. The vestiture is 
usually of medium length and hairy, though the species of Ravinia 
always have bristles present, those of Sarcophaga rarely. The size 
of the anal area is, to some extent, correlated with the extent to which 
the posterior surface is flattened, that is, the larger the anal area the 
larger the flat surface. In Ravinia an impressed line extends upward 
from it, apparently the remnant of a line of fusion between sides of a 
much larger anal area that has become small. This is also indicated 
by the more extensive flattened surface that is generally found in 
species with this area small. In Sarcophaga the upper limit of the 
anal area may be below, at, or above the center of the posterior sur- 
face. Some species show a main membranous area \Adth a small 
U- or V-shaped prolongation extending upward from it. The upper 
limit is considered to be marked by the upper limit of this prolongation, 
and as suggested for Ravinia probably indicates fusion. 
