114 HETERONEREIS. 
pair, globular in shape, is situated dorsally, with the lens 
directed upwards; the anterior pair, elliptical in shape, is 

Figs. 1 and 2. Anterior part of the body. 
Fig. 1. Dorsal view; fig. 2. Ventral view. 
for the greater part situated ventrally, having its lens 
directed downwards. As suggested by Gravier, these pelagic 
worms probably are swimming as easily on their back as 
on their belly. 
The two antennae, usually situated in front of the 
prostomium, are totally displaced to its ventral side at 
some distance from the anterior end, directed with their 
tips backwards. Also the palps, emerging in other species 
at the sides of the head and consisting of a large basal 
joint and a short terminal one, are entirely concealed 
under the head and possess a small proximal part and an 
elongated, conical, distal one; in the California-species these 
joints seem to be short and blunt. The upper pair of 
tentacular cirri appear to be broken off at their base and 
therefore it could not be stated how far they extended back- 
wards, whereas in the California-species they reach about 
the 16% segment; the inferior pair is the shortest and 
extends only to the 4'* segment. All these cirri are annu- 
lated over the greater part of their length. Like in other 
Heteronereis-forms the ventral and dorsal cirri in the an- 
terior region of the body show some modifications; in the 
anterior 4 segments the ventral cirrus is gibbous near its 
distal end, whereas in the anterior 7 segments the dorsal 
cirrus is not only much elongated, but also enlarged in 
front of the tip, that is bent downwards (fig. 3). The lip 
Notes from the Leyden Museum, Vol. XX XIII. 
