10 THE VOYAGE OF H.M.S. CHALLENGER. 



73. Myzostoma longicirrum, n. sp. (PI. I. fig. 4). 



In the circular form of the body, in the crenate character of the sharply defined and 

 hyaline marginal fringe, as also in the topographic distribution of the organs, this new 

 species resembles Mysostoma crenatum (Report, pi. vii.). The well-developed parapodia 

 (p) lie halfway between the margin and the middle of the body, the mouth (m) is almost 

 in the same line, and the comparatively small round suckers (s) are situated halfway 

 between the insertions of the parapodia and the margin of the body. The most striking 

 feature in this form, the disc of which has a diameter of about 1 '25 mm., is the development 

 of the cirri, of which the first to third and eighth to tenth pairs appear extraordinarily 

 elongated, but not uniformly, while the shortened fourth to seventh pairs are of equal 

 length, as the following measurements show : — 



There are furthermore slight difierences between the cirri of the same pair, especially 

 in the tenth. 



The single specimen was much damaged, and the figure given is thus to a large extent 

 a restoration. 



It was found on Actinometra parvicirra, Mtill. sp., from Samboangan (Challenger 

 Expedition). 



74. Myzostoma amhiguum, n. sp. (PL IL fig. 1). 



This form recalls at first sight Myzostoma antennatum (Report, pi. viii.), but 

 difiers from it not inconspicuously in tliis, that both posteriorly and anteriorly there are 

 two pairs of elongated cirri. The anterior and posterior ends of the body are so 

 like one another, that it is necessary to examine it by transmitted light, in order 

 to distinguish the two extremities. It measures 1-4 mm. in length, and the maximum 

 breadth is 1-1 mm. The diniensions of the cirri can be given only approximately, since 

 many of them are torn away (as indicated in the restoration by the lighter lines), while 

 others are too much twisted to admit of exact measurement. The short cirri of the 

 third to eighth pairs have a maximum length of O'S mm., the first pair 0*54 mm., the second 

 07 mm., the ninth 0-8 mm., the tenth 1 mm. The colour is a bright yellowish-brown. 

 The stomach branches {i) and ovaries leave only a narrow marginal fringe free. The mouth 

 (m) is situated on the border of the latter, and behind it is seen the muscular bulb of the 



