488 
THE VOYAGE OE H.M.S. CHALLENGER. 
In one example (viz., that having no ventral furrow in this part) the anterior 
region has eight bristle -tufts, and in the other ten pairs of l)ristles occur. The dorsal 
group in each tuft consists of elongated bristles (PI. XXIXa. fig. 20) with narrow 
wings and tapering tips ; while the inferior have short tips with broader wings 
(PI. XXIXa. fig. 21). The extremities are hardly broad enough to lie fiat, and 
hence are generally seen in profile, as in the figure. Similar proportions exist in the 
posterior group, though the tij)S of both kinds are much attenuated. 
The anterior uncinigerous rows do not fill the space between the 1)ristle-bnndles 
and the ventral scutes so completely as in Potainilla, a considerable interval occurring 
next the scutes. The hooks (PI. XXIXa. fig. 22) present a boldly marked dorsal 
convexity, a distinctly serrated and long crown which encroaches on the base of the 
great fang. The posterior basal projection is short, and the majority present a 
slightly downward curve at the tip. The basal or ventral line is inflated in front of 
the foregoing curvature. The body of the hook is more or. less striated. Those near 
the tip of the tail present a somewhat shorter base, and the serrations on the crown are 
more evident. 
Amongst the fine mud in the alimentary canal are a few Diatoms, fragments <jf 
sponge-spicules, minute Glohigerince and other Foraminifera. 
No tube is present. 
The body-wall in the anterior third agrees in the main with that of Sahella 
pavonma. The hypodermic pad has a deep median fissure, and, as in the species 
mentioned, a canal. Moreover, small blood-vessels appear in the basement-layer 
beneath the hypoderm. 
Sabella assimilis, n. sp. (PI. XXIXa. figs. 23-25). 
Habitat. — Dredged at Station 320 (off the South American coast, near Buenos Ayres), 
February 14, 1876; lat. 37° 17^ S., long. 53° 52' W.; depth, 600 fathoms; bottom tem- 
perature 37°'2, surface temperature 67°'5 ; sea-bottom, green sand. 
The specimens are small, reaching about 30 mm. in length and D5 mm. in diameter 
anteriorly. 
The body presents the ordinary shape, the ventral furrow proceeding forward to the 
second scute behind the anterior region, which (scute) it splits to the right of the median 
line. No furrow occurs on the dorsum. The cephalic collar anteriorly has dorsally a some- 
what long triangular flap on each side, then it diminishes toward the ventral border, 
which it barely touches before disappearing. The number of segments in the anterior 
region is variable, one example showing seven, the other eight. 
The pale branchiae are proportionally long, and the radioles are devoid of any dorsal 
