69 



Resume. 



Species examined. 



I had specimens of the following species under examnation: — Myzostoma cirriferum. I.euclcart; host. Antedon 

 petasus, Dub & Kor. M. glabrum; host. A. rosacea (a few badly preserved specimens only). M. gigas, Lutken; 

 host. A. eschrichtii, Miill. (a few specimens amongst which one complemental male). M. giganteum, n. sp.; host. A. celtica, 

 Mar. M. graffi, n. sp.; host. A. celtica; and M. carpenteri; host. A. dentata. Say (A. sarsii, Dtib. S: Kor.). 



Mysostonm giganfenui, n. sp. (PI. I, fig. 3, 4.) 



This species very much resembles M. gigas, Lutken; in exterior as well as in its anatomy. It is, hov\ever. 

 distinguished b}- its more rofiust and not so flat bod_\-. The dorsal surface rises from the translucent margin much more 

 sharply, and is considerabh' more arcuate, whilst in M. gigas it is flatter, and its margin not so sharpl}- marked; so that 

 transversal sections of this species acquire, thus, a more lenticular appearance, which is further promoted b}- the ventral side 

 being, usualh', cjuite flat (PI. IX, fig. ij, whilst in M. giganteum it is, usualh', not a little concave (PI, II, fis;. i . 



The thickness of the body is dissimilar m the two species ; in one specimen of M. giganteum (4 mm. l)road) the thickness was 

 I mm.; whilst one specimen of M. gigas (4 mm. broad) had a thickness of onl_\' 0.6 mm. In M. giganteum, the ventral side 

 is without an}" prominences ; whilst the specimens of M. gigas examined had, on their ventral side, a slight longitudinal pro- ■ 

 minence in which the ventral nerve-cord, especially the middle, is partl\' situated ; it becomes, thus, in greater or sm.iller degree, 

 a convex ventral and a concave dorsal surface (PI. IX, fig. 1} as well as. also, thinner; whilst the \entral cord of M. gigan- 

 teum is convex on lioth sides, consideralil}' thicker, antl is separated from the ectoderm l.)\- a considerable muscular layer PI. 

 II, fig. 1). From this mesial longitudinal prominence in M. gigas, similar slight ridges radiate, one to each parapodium; these 

 are caused b}- the musculi centrales; nothing similar is to be seen in M. giganteum. Both species have, on their dorsal sur- 

 face, tubercles distinguishable b\' the naked e\-e. The dorsal surface, in M. giganteum, appears to be a little more wrinkk\l, 

 and its parapodia are stronger and have a thicker and broader Ijase than those of M. gigas. The situation of the parapodia, 

 and the segmental glandulous sacks ') is similar to that of M. gigas. The gland openings are oval, and considerably 

 prominent, with radial furrows proceeding from them. The cirri appear to lie a little longer, and not so deeply recessed 

 as they are in M. gigas. The size appears to be about the same in both species. The largest specimen of .M. giganteum 

 examined was 6 mm. in diameter. The colour approaches to madder-brown, darkest in the middle, and paler and more \'ellowish 

 towards the margin of the body. In its anatomical structure, this species is distinguished from M. gigas bj- its having a 

 considerably more developed proboscis, and b}- the greater extension, and the peculiar form of the hook-glands; these are 

 separated into two branches, the one surrounding the hooks (chief hook, supporting rod, and reserve hooks",, and the 

 other; in which there is a number of \-acuoli; extending towards the middle of the body PI. II. fig. i,h., k'.i. '1 he hook- 

 apparatus appears, also, to be a little more developed. From the posterior part of the stomach in both, M. giganteum .as 



well as, also, in M. gigas, onl)' two intestinal branches issue (PI. IX, fig. 19J. Host. Antedon celtica. Marenzeller 



(Sladen). From Station 343, of the Norwegian Xorth-Atl.mtic Expedition (Neighbourhood of Spitzbergen, Depth 743 fathoms. 

 Temp. — 1.2 (Celsius). 



The species is one of the little migratory ones ; all the specimens found were seated, on the disk of the comatula. 

 close to the mouth. One complemental male was found under the ventral side of one of the largest hermaphrodites 

 measuring about '/■, of its length. 



Myzostoma graffi, n. sp. (PI. I, fig. 1, 2.) 

 This species resembles M. marginatum, but is distinguished b}- its tongue-indented margin, and b_\- the 20 cirri 

 situated, one upon each of the 20 tongues of the margin (PI, I, fig. i). The colour approaches to madder-l)rown, as in the last 

 mentioned species. The largest specimens measure up to 4.5 mm. in length. The l)nd_\- is of moderate thickness and cir- 

 cular in shape, with an arcuate dorsal surface and a translucent margin. The length i)f the cirri varies much, according as 

 they are more or less retracted, F'xclusive of the tongues upon which they are situated, they measure o. 19— 0.22 mm. 

 in length. The dorsal surface is, usuall\-, wrinkled anil beset with tu mercies. The parapodia are situated nearer 



') What previous wrilcrs have designatei\ suckers, I call l>y this, I,, my miiul, iiktc correct a])pellatioii. 



