OPISTHODONTA PTEROCHATA. 455 
from above, their bases fused with the head and their tips having slender papille. Nuchal 
organs between the head and the buccal segment, which is distinct from the head and bears 
two pairs of smooth tentacular cirri. Body 2—5 mm. long ; segments twenty-three to thirty- 
one or more; widest in the proventricular region, tapering slightly toward the head and 
more distinctly posteriorly. Anal segment with a short slender median, and two short 
lateral cirri. Proboscis short, straight and broad ; proventriculus is massive, extends over 
six segments, and has forty-eight rows of dots. Feet prominent, with a patch of cilia above 
each, and the six anterior segments differ from those behind. Dorsal cirri of all are long, 
cylindrical and smooth ; ventral cirri long and spring from the extremity of the setigerous 
lobe, which is blunt, with two thick spines. Dorsally is a simple bristle, curved distally 
and winged. Compound bristles short, thick, the ends of the shafts having three or four 
blunt teeth, the terminal pieces are bifid and coarsely serrated. The setigerous lobe and 
the bristles vary posteriorly, bemg more slender. A mature example carried ova from the 
twelfth segment. 
SYNONYMS. 
1914. Streptosyllis bidentata, Southern. Proc. Roy. Imish Acad., vol. xxxi, No. 47, p. 28, pl. iii, 
figs. 4 a—r. 
1921. 3 s McIntosh. Ann. Nat. Hist., ser. 9, vol. vii, p. 306. 
Habitat —Dredged in 24 fathoms in Clew Bay, on a bottom of sand and shells. 
The structure of the simple, serrated winged bristle recalls that of Stawrocephalus. The 
species differs from S. varvans in the length of the proboscis and proventriculus, in the monili- 
form condition of some of the dorsal cirri, in the larger palps, in the minute structure of the 
bristles, and in the greater number of the anterior segments with thick spines. It differs 
from S. Webstert in having six segments in the anterior region and in the structure of the 
bristles (Southern). The foot (Plate CXXXVII, fig. 3) has dorsally a simple bristle curved 
distally and winged. The compound bristles are short, with three or four blunt teeth at 
the end of the shaft, the distal piece being bifid and coarsely serrated. 
Genus OpistHoponta, Langerhans, 1879. 
Palps separate ; single tooth behind middle of proboscis ; smooth unjointed cirri and 
tentacles. Reproduction direct. 
OPISTHODONTA PTEROCHATA, Southern, 1914. Plate CXX XVII, fig. 4—foot and bristles. 
Specific Characters—Head rounded in front; four large reddish eyes with lenses ; 
median tentacle absent, arises between the anterior eyes; lateral tentacles near front margin ; 
palps free distally, united at the base. Buccal segment distinct dorsally, with two pairs 
of tentacular cirri, the dorsal twice the length of the lateral tentacles. All tentacles and 
cirri smooth and cylindrical. Body fragmentary, 6 mm., with forty-nine segments, tapered 
anteriorly. Pharynx dark brown, stretching through sixteen segments, and bears a sharp 
lateral tooth behind its middle. Proventriculus long and cylindrical, occupying eleven 
