REPORT ON THE MYZOSTOMIDA. 13 



The almost circular body has a diameter of 2*2 mm., and bears on its margin twenty 

 cirri up to 0"17 mm. in length. So far there is no difference between this form and 

 Myzostoma pentacrini, unless indeed in the fact that the body is somewhat less thick, 

 and seems to be flattened out, so that only posteriorly and on the left side is there any 

 curvature towards the dorsal surface. The mouth occupies, however, a subterminal 

 position on the ventral surface, from which the short, broad, cloacal tube (fig. 4, cl) also 

 arises. The parapodia (p) are furthermore considerably stronger than in the former, the 

 male genital papilla ( ^ ) is distinctly demonstrable on both sides, and the suckers are 

 represented by shallow grooves with radial folds (s). 



In addition to these points of difference, the intestine does not exhibit that extra- 

 ordinarily abundant branching which is seen in Myzostoma pentacrini. The branches 

 extend, however, close to the margin of the body, and in consequence of the marked 

 expansion of the csecal terminations appear to be closely packed. 



78. Myzostoma platypus, n. sp. (PI. III. figs. 7-12). 



P. H. Carpenter sent me a Myzostoma cyst with the accompanying note: — " Among 

 six individuals of Actinometra nohilis from Samboangan, I find one with some struc- 

 tures on the disk that I now recognise as Myzostoma cysts, though I did not know 

 them in 1878. They seem to have no plating whatever, which is curious. I send you 

 one with the Myzostoma inside which I cut from a corner where the disk was torn ; and 

 I shall have another part of the disk with a group of cysts drawn by my best artist.^ 

 They are always close to the ambulacral grooves and most frequently open into them, I 

 suppose in order that the Myzostoma may get hold of some of the food particles which 

 are travelling towards the mouth." 



The cyst is figured in figs. 7 and 8, from the ambulacral surface, and from the side. 

 The wall really exhibits no calcification and consists exclusively of a thin, dehcate, 

 readily phable skin. It is transversely expanded below the ambulacral groove, and 

 exhibits, close beside the latter, a slit-like aperture, through which the Myzostoma can 

 be seen {a). The animal lies within the cyst transversely to the ambulacral groove, and 

 the portion (a) which is seen in fig. 7 is the anterior end of the dorsal surface. The 

 body is bent dorsally both in front and behind, so that the ventral surface has a 

 markedly convex curvature. The latter lies close to the external convex wall of the 

 cyst, and is attached to the same by means of the parapodia. The character of the 

 ventral surface in this Myzostoma is very remarkable. In the first place, in the median 

 line there is a conspicuous row of five raised, longitudinal ridges (fig. 9, 1 to 5). Their 

 free surface is somewhat broadened and separated by sharp margins from the side, which 

 slopes down to the surface of the body. These ridges, and also the parapodia 



I See the forthcoming 'Report on the Crinoidea, Part II., pi. Ixv. (Zool. ChaU, Exp., part Ix.). 



