A NEW SPECIES OF MTZOSTOMA. 445 



The very delicate body is in the form of an oval plate, 4-6 millims. long and 3 rnillims. 

 wide. Its thickness is very slight, hardly as much as in the European Myzostoma cirri- 

 ferum ; and it is therefore fairly transparent, not only in the clear yellow marginal 

 portion, but also in the somewhat thicker and darker central part within the ring of 

 parapodia. The edge of the body is so much folded over towards the ventral side that 

 the animal appears convex when viewed from above, and concave as seen from beneath. 



The unusually extensive ramifications of the digestive canal * almost reach the edge 

 (PI. LII. fig. 19) ; and the marginal portion, which is free from them, is not sharply 

 marked off from the rest of the disk. 



There are 20 cirri (<?.), disposed at tolerably regular intervals from one another, except 

 that the ninth and tenth cirri on each side, and also the two of the tenth pah*, are some- 

 what more widely separated. As regards the length of the cirri, the last pair, with a 

 length of 077 inillim., and the first pair, 0'6 millim., are the best developed. The lateral 

 cirri vary in length from (>14 millim. to 46 millim. The ventral longitudinal furrow 

 is well defined in most of them. 



The body-wall bends slightly outwards between every two cirri, as is especially evident 

 in those parts which are not folded over; and the cirri, which are really marginal, tbus 

 come to lie in little bays within the edge. 



The circlet of relatively weak parapodia (p.) is situated about halfway between the 

 centre and the edge of the disk, though the fifth pair is much farther from the hinder 

 end than the first pair from the front end. The parapodia reach 077 millim. in length, 

 when extended ; but there is nothing special either about their form or about the hooklets 

 which they enclose. On the other hand, there is a peculiarity of structure, hitherto 

 observed in no other Myzostoma, in the finger-shaped process (p.c.) which each para- 

 podium bears at its base on the side turned towards the middle line of the body. This 

 process is markedly distinguished from the marginal cirri by the want of a glutinous cell- 

 groove (" Klebzelle "). It is therefore best designated as a parapodial cirrus ; and its 

 function is probably that of a tactile organ, as with the similarly shaped structure in the 

 Chaetopods. The 8 suckers (s.) occupy a line situated about halfway between the bases 

 of the parapodia and the edge of the disk. They are very flat, and but slightly pro- 

 minent, having a somewhat elongated shape, and reaching 023 millim. in length and O'l 

 millim. in width. 



Almost at the same level with the suckers is the ventral mouth-opening (m.), situated 

 0-35 millim. from the anterior end of the body. It leads into a considerably retracted 

 pharynx, the bulbus musculosus of which (ph.) reaches the unusual length of T23 

 millims. I could not make out the origin of the individual intestinal diverticula from 

 the central stomach (st.) ; but the rectum (»■.) is easily distinguished, together with the 

 oviduct (od.), which lies above it, and is filled with ova. The cloacal opening (cl.) is 

 placed terminally in a slight incision at the hinder end of the body. The two openings 

 of the male genital organs ( 6 ) are simple insignificant clefts close to the outer side of 

 the bases of the third pair of parapodia. 



* These are indicated in a semidiagranrmatic manner on the left side of the figure oiuy. 



