KEPOET ON THE ANNELIDA. 
527 
line, and are of considerable bulk, tbougb not massive. The longitudinal ventral 
muscles, again, are peculiar in having much hyaline connective tissue mingled with the 
fibres. The nerve-cords are widely separate in front, but appear to approach more closely 
posteriorly. The preparations, however, are unsatisfactory from softening, and it is 
observed that a special disposition must exist since the ventral muscles nearly meet in 
the middle line. The perivisceral chamber is dilated with the reproductive elements. 
The fact that the alimentary canal is distended with siliceous sand also makes the sections 
less distinct. 
Placostegus tridentatus, 0. Fabricius. 
Habitat. — Dredged in the “Knight Errant,” Station 5, August 11, 1882; 
lat. 59° 26' N., long. 71° 19' W.; bottom temperature 45°'4, surface temperature 50°'6; 
depth, 515 fathoms. 
Hydroides, Gunner. 
Hydroides midtispinosa, Marenzeller (PI. XXIXa. fig. 26, 27 ; PL XXXIXa. fig. 12). 
Hydroides midtispinosa, Marenzeller, Siidjapan. Annel., Denksclir. d. k. Akad. d. Wiss. Wien, 
Bd. xlix. p. 216, Taf. iv. fig. 2, 1884. 
Habitat. — Dredged off Kobe, Japan, in 8 to 50 fathoms. 
The specimen is fragmentary, and somewhat less than an average example of 
Hydroides norvegica. 
The branchise resemble those of the latter species, but the tapering filiform process at 
the tip is much shorter. The oj^erculum is also constructed on the same plan, with an 
inferior cup cut into numerous segments. The upper spinose circle, again, has fewer 
processes, eleven only being present (Marenzeller gives twelve), while in Hydroides 
norvegica there are nineteen. They are, however, more slender (PL XXXIXa. fig. 12). 
The body is too much injured to afford minute characters, but the cephalic collar 
probably resembles that of the ordinary species. The bristles (PL XXIXa. fig. 26) have 
decidedly less attenuate and elongate tips than in Hydroides no7'vegica, and the wing is 
more distinctly serrate at the edge. 
The anterior hooks (PL XXIXa. fig. 27), again, instead of having only five teeth above 
the great fang, as in Hydroides norvegica, show seven, so that the appearance of the 
edge is complex, the teeth being smaller and more numerous. The body of the hook is 
crossed by striae, nearly at right angles to the direction of the teeth. The prow is 
obtusely truncate ; and the dorsal line forms a larger angle than 90° with the ventral. 
The posterior hooks, as far as could be ascertained, have five or six teeth, which, 
moreover, appear proportionally larger than those in front. 
