454 STREPTOSYLLIS BIDENTATA. 
number of the anterior segments, with thicker spines, shorter and thicker bristles, and shorter 
terminal pieces; simple bristles dorsally; ends of the shafts presenting several teeth ; 
ventral cirri long in the posterior segments. Reproduction direct, with a pelagic stage. 
STREPTOSYLLIS WEBSTERI, Southern, 1914. Plate CXXXV, fig. 12—head and anterior 
region ; 12a—bristles. 
Specific Characters—Head broader behind than in front; eyes four, large, rounded, 
reddish brown, with lenses; median tentacle absent; lateral tentacles sprmg from the 
front of the head, smooth and cylindrical, shghtly narrowed at the base; palps small and 
filiform, ventral. Cillated nuchal organ between the head and the buccal segment, the 
latter having a pair of smooth tentacular cirri on each side, longer than the lateral tentacles, 
but shorter than the anterior dorsal cirri. All the cirri have rounded, faintly yellow granules 
internally. Body 3—5 mm. long, and having thirty-two to forty-nine segments ; proboscis 
straight and broad, dark reddish-brown, unarmed, and occupies three to four segments. 
Proventriculus extends over four to five segments, and has about fifty rows of dots. The 
anal segment bears a median, and two short lateral cirri. 
Synonyms. 
1914. Streptosyllis Webstert, Southern. Proc. Roy. Insh Acad., vol. xxxi, No. 47, p. 26, pl. u, 
fies. 3 A—F. 
1921. = . McIntosh. Ann. Nat. Hist., ser. 9, vol. vin, p. 305. 
Habitat.—Ballynakill and Bofin Harbours, in bottom tow-net (Southern). 
The head (Plate CXXXYV, fig. 12) has the outline indicated in the specific characters. 
Feet prominent, five characterising the anterior region, the spine in the first segment being 
thin, as in the posterior segments. In segments 2—5 the spines are large and thick. A 
single simple bristle is present in the dorsal region throughout. At the sixteenth foot the 
setigerous lobe is smaller, but the ventral cirrus 1s longer than in the anterior region.  Bristles 
(Plate CXXXV, fig. 12a) im segments 1—5 shorter and thicker than in the others. Behind 
these the bristles are thinner, have serrate terminal pieces, and the end of the shaft is 
serrated on one edge and has four sharp lobes, whilst the spine is slender with a bulbous 
tip. Capillary bristles begin at the 11th segment and extend almost to the tip of the tail 
in the mature males (the only forms found). 
Southern states that this species is most closely allied to S. varians, De St. Joseph. 
It resembles it in having five setigerous segments in the anterior region, and in having simple 
tips to the compound bristles. It differs in the presence of a slender spine in the first seti- 
gerous segment, in the shape of the terminal pieces of the anterior bristles, in the occurrence 
of simple dorsal bristles in all the segments, im having three anal cirri, and in other details. 
These differences, however, require further investigation. 
STREPTOSYLLIS BIDENTATA, Southern, 1914. Plate CXXXVII, fig. 3—foot with bristles. 
Specific Characters—Head broad, the width exceeding the length; four large eyes 
with lenses, the median tentacle arisimg between the anterior pair; palps ventral, invisible 
