422 
THE VOYAGE OF H.M.S. CHALLENGEE. 
split and fringed at the tip from wear. The intermediate forms have very fine filiform 
extremities, which appear to be nearly smooth, so fine are the minute spikes. The small 
ventral tufts in the same region have a similar shape, the tips being much fringed. The 
delicate intermediate forms present also extremely elongated filiform extremities with 
barely discernible microscopic spikes. 
The ventral bristles of the posterior region, so far as seen in the fragment, follow the 
same type as in the anterior region, only the more delicate series are so finely spinous 
toward the tip that they appear almost smooth under a power of 350 diameters. The 
same proportion, indeed, in this respect takes place as in the former series. 
The hooks (PI. XXVIa. fig. 15) have about nine teeth, the lowest, that next the 
point of attachment of the tendons, being long and distinct. The outline of the organ 
differs from that in either of the preceding. 
The anterior third of the body-wall in section conforms for the most part to the fore- 
going type. The hypoderm is comparatively thin, and is best seen on the ventral surface. 
The dorsal muscles are somewhat pear-shaped and widely separated. Their form is 
preserved by an environment of fibres from the circular and oblique coats. The 
ventral are more extended, and have the nerve and neural canal at the inner angle. 
The massive part of each muscle being external, the body naturally acquires a somewhat 
quadrangular shape in section. The alimentary canal is firm and rounded, its position 
in this region being maintained by various radiate bands of fibres. Two conspicuous 
dorsal vessels and a median ventral are present. 
The Lygdamis indicus,^ Kinberg, from Banks Strait, if the interpretation of what 
lie calls the “ operculum ” be correct, seems to approach the foregoing, and though it 
differs in the number of the “ opercular ” papillae, in the tips of the paleae and other points, 
the laxity of Kiiiberg’s description must be borne in mind. The Sahellaria IcBvispims, 
<drube,^ from Ascension, is also an allied form. 
Family Amphictenida:. 
The paucity of the examples of this family is remarkable, especially as the group is 
not confined to shallow water. The great depth (1600 fathoms) at which the species 
occur carries the bathymetrical range much beyond previous observations, for even in the 
Porcupine ” expedition the representatives of the family only reached 420 fathoms. 
Considerable variety exists in regard to the number of species collected by former 
expeditions. Schmarda gives only one, from Australia, and none occur in Kinberg’s 
scries. Grube again has five in his Philippine collection, but none in that of the 
1 Ofversigt Jc. Vetensk.-Akad. Fdrhandl., 1866, p. 350. 
Aimelidenausbeute von S.M.S. “ Gazelle,” op. cit., p. 542. 
