484 
THE VOYAGE OF H.M.S. CHALLENGER. 
to have been ample, as at the Bermudas and the Cape. A single example only comes 
from a depth of 600 fathoms, off the South American coast. The absence of Clione 
and Euchone from the collection of the Challenger is noteworthy. 
Claparede and others group this family with the Serpulidse, though the presence of 
a thoracic membrane covered with vibratile cilia characterises the latter. 
Langerhans, in his remarks on the Sabellidse of Madeira,^ gives a careful classification 
of the genera based on the occurrence of one or two rows of hooks in the thoracic 
region. Sabella, again, is distinguished from Potamilla by the presence of only one 
kiud of thoracic bristles, the latter having two kinds. 
Potamilla, Malmgren [Sabella, Linnaeus). 
Potamilla tovelli, Malmgren (PI. LIII. fig. 2 ; PI. XXIXa. figs. 16—19). 
Potamilla torelli, Malmgren, Nordiska Hafs-Annulater, p. 402 ; and Ann. Poly.chmta, p. 114, 
Tab. xiii. fig. 76. 
Habitat . — Dredged at Station 49 (south of Halifax, Nova Scotia), May 20, 1873 ; 
lat. 43° 3' N., long. 63° 39' W. ; depth, 85 fathoms ; bottom temperature 35°'0, surface 
temperature 40°'5 ; sea-bottom, gravel and stones. 
Length about 60 mm., and with a diameter of 2 A mm. anteriorly. 
The body is somewhat flattened dorsally and ventrally, especially posteriorly, where 
it is also tapered. The dorsal collar jDresents an anterior or inner sausage-shaped fold 
on each side, and a thinner posterior part which is not drawn to a point, but is slightly 
frilled in the preparations. This is continued straight to the ventral mesial line without 
a break, then forms a prominent triangular process on each side, a fissure intervening. 
A deep dorsal depression occurs between the frilled edges, but it is not continued 
farther backward than the second or third bristle-tuft. The anterior region of the body 
consists of eight segments, though occasionally there are only seven. The ventral 
median line divides the scutes from the tail forward to that behind the anterior region. 
It bends slightly to the right in the next posterior (making the divisions of the scute 
asymmetrical), then cuts off the right corner of that immediately behind the anterior 
region (ninth bristled segment) and disappears. A faint dorsal line exists anteriorly, 
but it is not depressed. 
The branchise on each side are from thirteen to fourteen in number, and, as usual, 
they are gracefully coiled in the tubes. So far as can be ascertained from the spirit- 
preparations, they seem proportionally long. Some are pale at the base and light 
brown at the tip ; others present pale rods and pale brownish pinnae throughout, the 
1 Zeitschr. f. wiss. ZooL, Bd. xxxiv. p. Ill, 1880. 
