198 Notes from the Gatty Marine Laboratory. 
processes, an operculum, the calcareous plate of which is 
rounded, whilst the anterior region has three pairs of 
bristles. The collar-bristles have the rather long tri- 
angular web at the commencement of the tip furnished 
with numerous small serrations, only the upper one or two 
being larger, a rather shallow gap above it, and a tapering 
blade with a finely serrated edge. These bristles thus 
approach those of Spirorbis granulatus and S. borealis. 
The third series appears to have sickle-shaped bristles. 
The tube has three sharp ridges and two grooves, the ridges 
differing from those of S. granulatus in their spinous: edge, 
aud the median ridge in some becomes deeper at the aper- 
ture, so that it forms a conspicuous keel, with a small sharp 
point over the circular aperture. 
4. On a Placostegus from the ‘ Porcupine’ Pen 
of 1870. 
The examples were dredged six miles from shore off Cape 
de Gatte in 60-160 fathoms in the ‘ Porcupine’ Expedition 
of 1870, attached to small stones. It is distinguished from 
the northern Placostegus tridentatus by the longer and more 
slender tube, which may be curved here and there but not 
coiled, and by the presence of three coarsely serrated ridges 
(a dorsal and two lateral). The three spines at the aperture 
also differ in character, since they are longer and curved 
outward. 
The thin diaphanous collar seems to have the same 
arrangement as in P. tridentatus, but the branchiz are pro- 
portionally longer and less numerous, viz., 11-12 in each 
fan, the filaments taper a little from base to apex, where a 
longer terminal subulate process than in the former species 
occurs. The long pinne, however, continue to its base. 
The opercular stalk is slender and remains nearly of the 
same diameter to the base of the vase-shaped operculum, 
which, though smaller, is more elegant in shape than in 
P. tridentatus. The truncated distal end is hollow and 
horny, the rim only being yellowish. 
The body is long and narrow, with six bristled segments 
anteriorly, and numerous posterior segments which are flat- 
tened toward the tail and end in an anus with a distinct and 
rounded papilla at each side. The six setigerous processes 
anteriorly have tufts of the same kind, viz., bristles with 
straight ‘shafts, very slightly bent tips waht ae wings, 
in which respects they do not materially differ from those 
of P. tridentatus. Posteriorly bristles seemed to be absent 
