REPORT ON THE ANNELIDA. 
521 
rise to a beautiful tessellated aspect, apparently from its occurrence in rliomboiclal 
nucleated cells, in regular rows and distinctly separated from each other. 
The operculum forms a circular, somewhat fragile and slightly concave, shelly disk 
coloured very prettily by radiate bands of a pinkish or salmon hue, broader at the 
circumference and narrower at the centre. The rim of the operculum is double, the 
outline between the two rings being concave. In one small example no less than four 
tiers of the opercular rim are present (PI. LV. fig. 3), the upper being smaller and less 
concave than usual. The operculum is supported on a stout peduncle with a broad wing 
at each side, terminating at the base of the region proper in a free conical process of 
the ordinary appearance. In one instance peculiar minute concretions occur on the 
tessellated epithelial surface of the wings, the rounded nodules being crystalline or spinose 
under the microscope. No rudimentary peduncle or operculum exists on the right side. 
The anterior region is composed of seven segments, each carrying a pair of setigerous 
processes. The first is considerably in front of the others, and dorsal instead of lateral in 
position. It is also very much smaller, and the l^ristles, which are less perfectly 
developed, have a different direction. The other six pairs are deep yellow, have straight 
shafts, with the tips distinctly bent and furnished with well-marked wings (PI. XXX Ia, 
fig. 26). The posterior bristles, again, quite differ, presenting broad extremities 
obliquely tapering to a long filiform process at one side (PI. XXXIa. fig. 27), and 
having the anterior or distal edge of the tip covered with spines, wdiich also pass along 
the shoulder or broad j)rocess. The shafts of these bristles are nearly cylindrical. 
The cephalic collar, which is continuous with the lamella passing backward beneath 
the bristle-rows on each side, presents a complex arrangement dorsally. A large frilled 
and fan-shaped process occurs at each dorsal angle, the outer edge being separated by a 
deep notch from the succeeding part. A peculiar region, having the aspect of a partially 
folded fan, comes next, a,nd is generally placed beneath the former in the ordinary 
condition in the preparations, while it also is separated by a deep notch from the rest. 
The collar is continued ventrally and crosses to the opposite side, the margin being 
cut into broad scallops, but showing no median fissure. The thoracic prolongations of the 
respective sides join together ventrally behind the last uncinigerous process of the region. 
Each thoracic uncinigerous row has a pigment-speck at the ventral end, just in front 
of its termination. The hooks (PI. XXXIa. fig. 28) are somewhat triangular in outline, 
and have about fifteen teeth above the inferior one (great fang) which is peculiarly 
bent upward. With the exception of the first (or upper) two the teeth are large 
superiorly, and gradually diminish toward the inferior end. The last process (corres- 
ponding to the great fang) follows a sim i lar direction at the base, but is curved upward 
at the tip. The dorsal line is comparatively long, and shows only a trace of an 
inflection a little below the middle. The basal line is somewhat convex and cuts off the 
anterior angle, so as to remove the usual projection. The body of the hook is boldly 
(ZOOL. CHALL. EXP.- — PAKT XXXIV. 1885.) LI 66 
