Gatty Marine Laboratory, St. Andrews. 189 
The next, or tenth, form, Spirorbis spirillum, L., is every- 
where abundant round the British shores on zoophytes, Fuci, 
alge, Corallina officinalis, Flustra, and other structures. The 
collar agrees with that in other Spirorbids in being widely 
split posteriorly, but continuous in front, Its connection 
with the membrane of the anterior setigerous region is also 
normal. The branchiz appear to be few, viz., four on each 
side, and the terminal processes of the filaments are short, 
so that they do not project beyond the pinne, which thus 
form a more or less even tip, since the distal pinne are 
short. 
The operculum forms a shallow vase with a foot or process 
beneath, the edge of the latter being crenate. There is no 
space for opercular embryonic development in this species. 
The body is widest in front, and gradually tapers to the 
tail whichis normal. The collar-bristles are characterized by 
the absence of the gap near the base of the terminal blade. 
They are comparatively small, have long straight shafts, 
which dilate on reaching the distal shoulder, the terminal 
region being sharply bent backward, tapered to a fine point, 
and rather coarsely serrated along the edge especially at the 
base. The other bristles conform to the usual type. The 
figure of the collar-bristle, as given by Miss Pixell*, from the 
Pacific Coast of North America, diverges considerably from 
the British form, the tip being shorter and broader. 
The second fascicle consists of simple winged bristles. 
The posterior bristles have the tips bent at an angle or 
“‘kneed,” and usually project little in the preparations. 
Few forms appear to have had greater vicissitudes in nomen- 
clature than the next, oreleveuth, species, viz., Spirorbis granu- 
latus, i., a form which essentially differs from the Spirordis 
granulatus,L., of Caullery and Mesnil +, from Greenland and 
Nova Zembla, since the globular form of the operculum, as 
figured by the French authors, no less than its ovigerous cha- 
racter, separate it from the present species, which, as Fleming { 
truly said in 1825, occurs “on old shells, but more frequently 
on the underside of loose stones about low-water mark, very 
common.” It is especially abundant on the rocks and 
stones in rock-pools at St. Andrews. The branchiz are 
pale, ten in number, and the cuticle of the filaments is thin, 
so that the hypodermic elements form the main support. 
