438 Proceedings of Royal Society of Edinburgh. [sess. 
disc-like; the latter is partly bowl-shaped, partly cylindrical. 
The worms are of small size. The following dimensions of four 
specimens may be regarded as typical : — 
No. 
I. 
II. 
III. 
IV. 
Total length of body, 
5'25 
4*3 
3-30 
4-3 
Diameter of widest part (anterior 
spiny region), .... 
2*00 
2*5 
2-05 
2*3 
Vertical height of anterior region, . 
175 
1-6 
1*9 
2*0 
Length of cylindrical tail region, 
2*68 
21 
1*2 
1-7 
Ratio of tail region to total body- 
length, 
•51 
•49 
•36 
•39 
Numbers 1 and 2, on subsequent examination, proved males, and 
3 and 4 females. 
The colour is dead white. The rostrum, which was found fully 
extended in only a few instances, is very nearly cylindrical, being 
rather thicker at the base than at the tip. In one specimen its 
length was found to be 1*14 mm., its width at tip T3 mm., and at 
the base - 23 mm. It carries about 28 rows of hooks, of which 
there are 10 in a row. These hooks differ slightly in form in 
different regions of the rostrum, but are quite evidently modifica- 
tions of one type (fig. 2). In the row nearest the tip they are 
slender, and point more directly outward than those do near the 
base. Here they are shorter and thicker. Actual measurements 
are — 
Hooks of first row . . T14 mm. long. 
Hooks at base of rostrum . ’07 mm. long. 
The rostrum at its base occupies the centre of a region of 
peculiar form. Here the anterior part of the body is conical, and 
from the tip of the cone the rostrum emerges. Around the cone 
at its base there is a shallow circular depression, the outer border 
of which rises to form a thickened rim. This rim marks the 
widest part of the whole worm, and defines the posterior border of 
the front body-region. The whole of this region — cone, depression, 
and rim — is covered with minute, slightly recurved spines, regularly 
arranged in rows. The average measurement of these spines is 
07 mm. in length. Behind this the body curves backward in a 
bowl-like manner, beyond which it is bent sharply at a right angle, 
and continued in a much narrowed tail portion. The free end 
differs slightly in the two sexes, as will be described. This posterior 
