REPOET ON THE MYZOSTOMIDA. 
57 
half their own diameter. The parapoclia are well developed, the cirri about '*09 mm. long. 
The difference between this specimen and that shown in fig. 3 consists principally in 
the larger size of the latter ; its body is about *9 mm. long (measured to the point X 
where the median caudal appendage takes its origin ; I could not find the cloaca) ; the 
length of the median caudal appendage is about 1*14 mm. As in the preceding species, 
the external caudal appendages are much smaller than the median ones. The median 
caudal appendages are grown together, while the exterior ones are free from their base up- 
wards. The length of the last cirrus on either side (c.) is *26 mm. ; the rest are scarcely half 
as long. In all other dimensions this specimen (fig. 3) agrees with the first described 
specimen, the size of the pharynx, the parapodia, and suckers being of course actually 
larger since the specimen itself is larger. 
Host. — Anteclon bidentata, P. H. C., Station 186 (Torres Strait) of the Challenger 
Expedition. 
52. Myzostoma quadricaudatum, n. sp. (PL Y. figs. 5, 6). 
The body is roundish and flat, light brownish in colour, and but slightly transparent ; 
it has a length of 1 mm. and a breadth of *9 mm., and bears twenty cirri, the first and 
longest pair of which measure *23 mm., the rest averaging *16 mm. The cirri are 
massive and end obtusely. The body terminates in four caudal appendages, every one 
of which contains an intestinal caecum. They are of equal length (*4 mm,), and end 
obtusely. The parapodia ( p .) are well developed, and contain strongly bent hooks 
(fig. 6); the round suckers ( s .) are situated upon the margin. On a level with the 
suckers, between the fifth and sixth cirrus on either side, is the male genital aperture ( $ ), 
at the bottom of a shallow furrow. The mouth opening is behind the anterior margin, 
the cloacal aperture is at the base of the bifurcation of the median caudal appendages. 
The extremely small size of the pharynx (ph.) is remarkable. 
Host. — Antedonjluctuans, P. H. C., from Station 190 (Arafura Sea) of the Challenger 
Expedition. 
53. Myzostoma lobatum, Graff. 
Myzostoma lobatum , Graff, Genus Myzostoma, p. 19, pi. il. figs. 3, 4. 
Host. — Actinometra Jimbriata, Mull., Bohol (Philippines). 
54. Myzostoma bicaudatum, n. sp. (PI. Y. figs. 2, 3). 
This specimen, which is the smallest of the Myzostomida Caudata, measures *45 mm. 
(without the caudal appendages) ; it is nearly circular in form, and flat on both sides. It is 
stout, hardly at all transparent, and brownish in colour ; there is hardly any trace of a 
thinner lateral zone. The twenty cirri arise from the ventral side of the margin ; in the only 
(ZOOL. CHALL. EXP. — PART XXVII. — 1884.) Ed. 8 
