50 
THE VOYAGE OF H.M.S. CHALLENGER. 
39. Myzostoma excisum, n. sp. (PI. VIII. fig. 2). 
This species is characterised by the deep excision of the hinder margin of the body, 
caused by the prolongation of the lateral parts beyond the cloacal papilla (cl.). The body 
is flat, strong, dark brown in colour, and slightly transparent only upon the marginal 
parts. The latter are prolonged into ten pairs of obtusely-pointed cirri, of which the last 
pair occupy the two ends bordering the notch. The hinder half of the body being the 
largest, the whole animal has a heart-shaped contour. That portion of the ventral surface 
which is enclosed by the suckers on either side, by the mouth in front, and by the cloacal 
papilla behind, is rather swollen and marked off from the marginal part. The parapodia 
(p.) are very large and well developed ; they are nearly as long as the radius of the body, 
and project beyond its margin. The large pharynx is protruded considerably beyond the 
mouth. The length of the specimen, from the anterior end to the cloaca, is # 8 mm., the 
length of the lateral portions 1 mm. the greatest breadth ’9 mm., the length of the 
largest cirri ’12 mm. Besides this specimen, which was dredged during the “Blake” 
Expedition, I examined a smaller one from the Kiel Museum, which measured only 
’54 mm. long. 
Hosts. — (a) Antedon hageni, Pourt., dredged by the U. S. S. “ Bibb” on the Alligator 
Beef, in 96 fathoms, May 6, 1868. 
( b ) Antedon impinnata, P. H. C., from Mauritius, North Bay, 15 fathoms, 
. belonging to the Kiel Museum. 
40. Myzostoma irregulare, n. sp. (PL IX. figs. 2-5). 
I include under this species, so named on account of the irregularity in the formation 
of the cirri, several forms, the strict affinities of which must be cleared up by future 
investigation. I shall at present describe every variety. 
(A) Fig. 2 represents, without doubt, the type of the species ; it was taken at 
Station 249 (Grenada) of the “ Blake ” Expedition. There are four individuals, all of 
which are delicate and yellowish in colour, with a transparent border ; there are ten pairs 
of longer cirri and a number of smaller wart-like secondary cirri arranged singly or in 
pairs between the others ; a single median cirrus ( c .) is situated at the hind end, and is 
very characteristic. The specimen figured is ‘8 mm. long, * 7 mm. in breadth, and the 
longest cirrus measures *12 mm. Another specimen measured 1*2 mm. in length, and 
IT mm. broad; the cirri were proportionately smaller, though actually larger than those 
of the last mentioned individual. In none of the specimens belonging to this group 
could any regularity in the arrangement of the smaller cirri be observed (see p. 8). 
The strongly developed parapodia (p.) occupy the middle region between the 
margin and the centre of the body, and the large oval suckers ( s .) lie between the para- 
podia and the margin of the body. 
