248 



Annelida Chcetopoda 



parts ; its outer margin obliquely truncated, thin, minutely 

 denticulated. The remaining setge 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 



