522 
THE VOYAGE OF H.M.S. CHALLENGER. 
striated nearly at riglit angles to the teeth. The posterior hooks are smaller than the 
foregoing, form a triangle with a more acute apex at the great fang (curved inferior tooth), 
and the number of teeth is smaller, viz., about thirteen, exclusive of the inferior process. 
In the alimentary canal of this form Coccoliths and Coccospheres are very abundant ; 
Diatoms, arenaceous and calcareous Foraminifera are also common ; while an occasional 
Entomostracan, Gregarina, and peculiar translucent pointed bodies like shuttles, trun- 
cated at one end, are comprised amongst the other organisms. 
The tubes, which are bound together, are massive, triangular in cross-section, and the 
dorsal keel is often roughly serrated. The aperture is little, if at all, dilated, is 
smoothly rounded internally, and externally marked by the terminations of the three 
ridges. The tube is streaked with a pinkish or salmon colour, which also tints the lips of 
the aperture. In one example two regularly arranged longitudinal rows of pores occur a 
short distance below the dorsal keel. 
Various commensalistic bodies, from Foraminifera to Mollusks, occur on the anterior 
end of the tubes, which thus appear to have been tolerably isolated. The species, 
however, may occur in larger masses. 
A form allied in the shape of the operculum is Pomatostegus boiverhankii, Baird, from 
Australia, but the hooks quite differ. The Pomatostegus cariniferus, Baird, is likewise 
dissimilar. Grube’s Pomatocerus multicornis,^ from the Red Sea, differs in the structure 
of the basal region of the operculum. Both this and Ehrenberg’s Pomatocerus sanguinea, 
however, are allied forms. 
Placostegus, Philippi. 
Placostegus ornatus, Sowerby (PI. LV. figs. 5, 6 ; PI. XXX a . figs. 25, 26). 
Habitat . — Trawled at Station 244 (in the deeps of the Pacific), June 28, 1875; 
lat. 35° 22' N., long. 169° 53' E.; depth, 2900 fathoms; bottom temperature 35°'3, 
surface temperature 70° ’5 ; sea-bottom, red clay. 
Also at Station 253 (further westward in the same area), July 14, 1875 ; lat. 38° 9'N., 
long. 156° 25' W.; depth, 3125 fathoms; bottom temperature, 35°’l ; sea-bottom, red 
clay. This specimen was attached to a nodule forwarded by Mr. Murray. 
And at Station 285 (in the abyss of the Pacific, midway between Sydney and 
Valparaiso), October 14, 1875 ; lat. 32° 36' S., long. 137° 43' W.; depth, 2375 fathoms; 
bottom temperature, 35° '0 ; sea-bottom, red clay. 
The length of the largest example (which is considerably shorter than the tube) is 
19 mm., with a diameter anteriorly of 1 mm. The diameter of the tube at the 
anterior aperture is barely 2 mm., and it tapers gradually to a slender point posteriorly. 
1 Anneliden des rothen Meeres, op. cit., p. 39. 
