REPORT ON THE MYZOSTOMIDA . 
71 
65. Myzostoma willemoesii, n. sp. (PL XIV. figs. 1-8). 
One of the Canada balsam preparations, which were made during the voyage by v. 
Willemoes Suhm, and sent me by Mr. Murray at the end of 1882, contained a large and 
a small Myzostoma, and was labelled “ Myzostoma , one pair from Coma tula- arm- cave, 
Kermadec.” The specimens were deeply stained with carmine, and no doubt much 
squeezed, as could be seen by the numerous folds. Although not much more than the 
contour of the animal could be observed (figs. 1, 2), it was evident that it was a new 
species. I received from Mr. P. H. Carpenter some additional material, which enabled me 
to study the form of the cyst. This species inhabits Antedon basicurva and Antedon 
incequalis, P. H. C., and causes the pinnules to become spirally twisted ; the margins of 
the spirals are in close apposition, forming a space in which the parasite lives, communi- 
cating with the exterior by an aperture at the point and by a fissure at the base. Pig. 6 
represents one of these malformed pinnules in Antedon incequalis, P. H. C., magnified five 
times, and fig. 7 shows the first three joints of this pinnule viewed from the inside (A) and 
from the outside ( B ). The ambulacral furrow is continued through the basal fissure into 
the interior of the cyst as far as its point. The single joints of the pinnule have, as may 
well be seen in fig. 7, a regular roof-shape, and each side, the one turned towards the arm, as 
well as the one turned away, is smooth and equal. In two cysts, however, of Antedon 
basicurva, P. H. C., and in one more than the other, the sides of the pinnule-joints that 
are turned towards the arm are longer than the others and irregularly notched (fig. 8, C). 
Each cyst contains a female and a male, the female being always the larger, and placed 
quite close to and with its ventral side attached towards the inner wall of the cyst. This 
species differs in many respects from the other dioecious cysticolous forms ( Myzostoma 
cysticolum, Myzostoma tenuispinum, Myzostoma injlator, Myzostoma murrayi), and recalls 
the typical free-living forms, in that both male and female are furnished with powerful 
suckers and ten pairs of long cirri. 
The femcde taken out of the cyst (fig. 6) is displayed in fig. 3, viewed from above, 
and in fig. 4 viewed from below. All the other cysticolous forms arc turned upwards 
on both sides ; but in this species it is the anterior and posterior ends of the body that 
are turned up, the mouth and cloaca therefore being also turned upwards. The diameter 
of the disk of the body, which is circular when extended, is 2 *8 mm., the thickness in the 
middle is about the same as in a full-grown specimen of Myzostoma glabrum, but becomes 
less towards the marginal portion, which is therefore somewhat transparent. The ten 
pairs of cirri are not greater than T5 mm. in length; the anterior parapodia, situated 
close to the mouth, are the smallest (fig. 3 ## ) ; the parapodia are arranged in two longi- 
tudinal rows nearer to the middle line than to the border, and are at quite equal distances 
from each other (fig. 4 ,p). They are small and obtusely pointed, T2 mm. long at the most, 
