REPORT ON THE ANNELIDA. 
525 
This specimen diverges in certain respects from either of the preceding. 
The branchiae appear to be similar, but the pinnae are decidedly longer, if the 
preparation is to be relied on. The tips of the radioles have smooth filiform processes. 
The operculum somewhat resembles that of Plcwostegus henthalianus, though the surface 
is less scooped in the example. Moreover, -it is borne on one of the branchial radioles, 
which is specially strengthened for its support, while clothed with pinnae up to the’ 
terminal dilatation below the opercular region proper. Another branchial radiole is 
somewhat thickened, and bears at the tip a clavate process, representing a rudimentary 
opercular development. 
The cephalic collar is incomplete, but a large rounded flap occurs on each dorso- 
lateral region. 
Most of the thoracic bristles are absent. In one tuft (apparently the second) two 
groups are present, viz., a series of slender tapering bristles, probably the dorsal, and 
another group of stouter bristles (PI. XXXa. fig. 29), with peculiar tips, a distinct 
shoulder occurring below a concavity or “ bite.” The former probably indicates the 
distal end of the shaft. When viewed antero-posteriorly an enlargement is also very 
evident at the upper end of the shaft, showing that it is thickened all round. 
The anterior hooks (PL XXXa. fig. 30) approach the foregoing forms in outline, but 
differ in possessing five teeth above the great fang, in having a sharper angle at the 
inflection of the dorsal line, and in possessing a proportionally wider base than either 
Placostegus ornatus or Placostegus henthalianus. 
The tube is not pentagonal, but from the presence of a deep groove on each side 
has rather a quadrangular appearance in transverse section, though the dorsal line is 
rounded (convex). It is somewhat wrinkled, but is devoid of the bold transverse 
ridges of Placostegus ornatus or the longitudinal toothed eminence of Placostegus 
henthalianus. 
Placostegus assimilis, n. sp. (PL LV. fig. 9 ; PL XXIXa. figs. 29, 30). 
Habitat. — Dredged at Station 33 (off the Bermudas), April 4, 1873 ; lat. 32° 21' N., 
long. 64° 35' W.; depth, 435 fathoms; surface temperature, 68°'0 ; sea-bottom, coral 
mud. 
The specimen is about the same size as the British Placostegus triclentatus, J. C. 
Fabricius. 
The branchiae appear to agree in form with those of Placostegus tridentatus, but they 
are longer. They also have a smooth filiform tip. The opercular region, however, difiers 
very considerably in shape. The dull yellowish operculum proper is less concave, though 
(A similar thickness and having the same brownish rim. Instead of the simple clavate 
