58 
THE VOYAGE OE H.M.S. CHALLENGER. 
specimen that I have they are nearly all cut off, but the stumps that have remained 
behind permit me to judge of their size. The longest cirrus (the first) measures T6 mm., 
the shortest (fifth on the right side) measures ‘03 mm. — commencing from the margin of 
the body. 
The two caudal appendages are round and massive, becoming gradually smaller and 
arising from the ventral side ; they end in an obtuse point. There is no terminal thread, 
and each contains an intestinal caecum. They measure - 3 mm. from the margin of the 
body to their tip. The slender parapodia (p. ) are prominent ; the hooks are slight and 
not much bent at the tip (fig. 3). The small suckers (s.) are closely approximated to the 
margin of the body, and are flat and circular. The pharynx is remarkably thick and 
large, and measures nearly two-thirds of the length of the body ; it extended some dis- 
tance beyond the subterminally situated mouth. The cloacal aperture is, like the mouth, 
ventrally situated near the hinder margin and between the insertions of the two caudal 
appendages. Of sexual organs I could discover no trace, but there were a number of 
eggs round the intestinal caeca within the caudal appendages, which appeared to be 
unripe, and therefore mark out this specimen as a young one. 
Host. — Actinometra meridionalis, A. Ag., sp., “Bibb” Expedition, January 16, 
1869, west of Tortugas. 
55. Myzostoma Jilicauda, n. sp. (PI. Y. fig. 4). 
This species resembles more closely Myzostoma bicaudatum than the other species 
with two caudal appendages, viz., Myzostoma jiliferum , firstly, by the strong development 
of these caudal appendages, and secondly, by the fact that the first and the last cirri are 
the longest. If it be really true that the terminal threads (see p. 8) appear with 
increasing age, it might well be supposed that this species is only an older stage of 
Myzostoma bicaudatum. 
Moreover, among the seven specimens that I examined, all of which came from the 
same host, there was one about one-third smaller than the specimen figured, which 
differed from the rest in possessing no short terminal thread upon the caudal appendages. 
The specimens, however, were not well enough preserved to enable me to state this fact 
with entire confidence ; possibly the terminal thread may have been torn off. In the 
meantime, therefore, I must consider Myzostoma Jilicauda as a distinct species. 
The largest specimen (fig. 4) was 1’3 mm. long, and in breadth somewhat less. The 
only caudal appendage (the left hand one had been torn off) is T9 mm. long, and about 
one-seventh of this length is occupied by the terminal thread (CF.) ; it is cross furrowed 
here and there (C A). The tip of the terminal thread was wanting, and I have endea- 
voured, by comparison with other specimens, to compute its length. The greatest 
diameter of the caudal appendage is '27 mm. ; it contains a terminal branch (i.) of the 
