36 
THE YOYAGrE OF H.M.S. CHALLENGER. 
situated in a shallow excavation on the margin of the body. The ventral surface is 
sculptured like the dorsal into polygonal areas, which are, however, irregular in size and 
form. The central muscular mass is marked by a low elevation (figs. 20, 21). 
The parapodia (p . ) are fully developed and situated at about two-fifths of the whole 
radius from the margin of the body; their muscles, especially the musculus centralis, are 
not strongly developed, as is aliso shown by the absence of radial elevations on the ventral 
surface of the body corresponding to them. The hook (fig.. 24, u .) ends in a fine short 
point, bent so little that it only forms an obtuse angle with the axis of the stem ('013 mm. 
large). The manubrium ( ma .) has a large stalk, which is of equal size throughout its whole 
length. At the extremity it is obtuse, and ends in two irregular swellings directed 
backwards. *The hemispherical suckers (fig. 20, s.) are small, but project somewhat. 
The mouth (m.) is placed very far back, nearly on a level with the insertion of the 
parapodia; the pharyngeal tube (ph.) projects from it; nearer to the margin .than the 
mouth is the cloacal papilla (cl.), at the posterior end of the body. 
The male genital papillae ( $ ) are high cones with broad bases. They are considerably 
larger than the parapodia, close to which they lie. 
The smaller individual is remarkably different from the one just described. It is 
oblong in shape instead of circular (fig. 23), and less convex on the dorsal surface; the 
portion of the body outside of the five pairs of elevations is gradually bent downwards. 
The median area lies in the same plane with these elevations, which are flattened and 
enlarged to five-sided masses, looking just as if the animal had been subjected to 
considerable pressure. The tubercles in the same way are flattened and polygonal, 
touching one another on all sides. The resemblance to tortoise-shell is almost more 
striking, since the median area is divided up by several transverse furrows. 
In other respects the two individuals agree, and since they came from the same host, 
I do not doubt that they belong to one and the same species. 
Host. — Actinometra lineata, P. H. C. Station 285 (Barbados) of the “Blake” 
Expedition. 
13. Myzostoma IvtJceni, n, sp. (PL II. figs. 20, 21). 
This unique specimen from the Copenhagen Museum measures rather more than 
3‘5 mm. long and 3 mm. broad. The anterior margin is slightly notched, so that the 
contour is almost heart-shaped. The body is very compact and quite opaque. The 
dorsal surface is greyish-brownish-black in colour, and divided by deep and shallow 
furrows, with numerous irregular areas like the bark of a tree. The cirri are twenty in 
number, 0’6 mm. long, and arranged at equal distances from each other, except the 
first pair, which are separated by an interval double as great as that between the others. 
The ventral surface is very characteristic. All the usual elevations are distinctly seen. 
The parapodia and suckers are well developed ; the latter project between the parapodia 
