48 Annelida Chcetopoda 
parts ; its outer margin obliquely truncated, thin, minutely 
denticulated. The remaining setae of this segment are of 
the same form as those found on the other segments. 
Middle region. Dorsal ramus, composed of two ventral 
plates, of which the inner is bilobed, and arises just out- 
side the middle line of the dorsum (f 99). This plate is 
connected at base with a similar vertical lateral plate, 
which, however, is not lobed, and does not contain setae. 
The lips of the ventral ramus are anterior and posterior; 
both are connected with the latero-dorsal plate by a basal 
membranous prolongation. The posterior lip is a low, 
arched plate, running downward nearly to the middle line 
of the ventral surface. The anterior lip is much shorter 
than the posterior, arising just above and in front of the 
latter, also a little in front of the latero-dorsal plate. Both 
lips of the ventral ramus have a yellow color derived from 
the uncini concealed within them. 
Posterior Region. The dorsal rami are vertical (f. 100), 
swollen at base, otherwise cylindrical, terminating in a 
button. They are close to the middle line of the body, and 
contain from four to six very delicate setae, which project 
slightly. The ventral rami are the same as in the middle 
region, only the lips are much reduced in size, and very 
close to each other. 
The anal segment is without appendages, conical, ob- 
liquely truncated from above downward,' divided below 
into lobes which can not be seen from above. 
Dorsal sulcus, bordered on each side by a delicate raised 
membrane. These may be revolute, leaving the sulcus 
open ; or their edges may be brought together, completely 
closing it. Sulcus densely ciliated. 
The body tapers uniformly, the diameter of the anal 
segment being about one-third that of the anterior part. 
Anterior region, convex below and laterally; flat or 
