524 
THE VOYAGE OF H.M.S. CHALLENGER. 
from the infero-lateral region to the median line. These muscles are composed of a 
number of very fine, closely arranged plates which give a regularly striated apjDearance 
to the in section. The muscles are most bulky interiorly. The ventral region 
presents two prominent curved ridges, and an intermediate hollow. In the former the 
longitudinal ventral muscles are situated, and they are of consideral^le size, notably 
exceeding those in the previous genus. A long hiatus exists between them. The body- 
cavity was so distended with reproductive elements that the nerve-cords could not be 
seen distinctly, but they appeared to be in their usual position at the inner border 
of the muscles. 
Placostegus hentJialiamis, n. sp. (PI. LV. fig. 7 ; PI. XXXa. fig. 28); 
Habitat. — Dredged on the nodule forwarded by Mr. Murray at Station 253 (Mid 
Pacific), July 14, 1875 ; lat. 38° 9' N., long. 156° 25' W. ; depth, 3125 fathoms; bottom 
temperature 35°T, surface temperature 67°'7 ; sea-bottom, red clay. 
The specimen is cpiite fragmentary, so that a minute description is unattainable. It 
is smaller than the foregoing, the "widest portion being only a little more than 1 mm. 
The branchiae seem to approach those of Placostegus ornatus in forming a somewhat 
truncated outline in 'mass, and in possessing a smooth free filament at the tip of each 
radiole. The operculum constitutes a hollow platter with a yellowish-brown rim, carried 
upon the summit of a hollow process, shaped like a wine-glass. The peduncle is 
dilated distally, and forms a kind of shoulder at its junction with the former region. 
The bristles of the anterior region are similar to those of the preceding species, 
presenting a long and very attenuate tip, with a bend where it joins the shaft j and 
distinct wings. 
The anterior hooks (PL XXXa. fig. 28) differ from those of the former species in 
outline. Only four teeth occur above the great fang. The prow beneath the latter is 
much better developed than in Placostegus ornatus, and the concavity in the dorsal 
outline is deeper. 
The tube of this form is pentagonal, the three upper ridges especially being pro- 
minent, and armed with a series of blunt teeth, which posteriorly (at the smaller end of 
the tube) disappear, leaving only slightly rugose ridges. One surface, as in the preceding, 
has been attached to the nodule. 
Placostegus mbrchii, n. sp. (PI. LV. fig. 8 ; PI. XXXa. figs. 29, 30). 
Habitat. — Trawled at Station 285 (in the Pacific, mid- way between Sydney and 
Valparaiso), October 14, 1875 ; lat. 32° 36' S., long. 137° 43' W. ; depth, 2375 fathoms; 
bottom temperature 35°’0, surface temperature 65°'0 ; sea-bottom, red clay. 
