1905.] AXB ECHIURTDS OF THE ''sKEAt" EXPEDITION. 3^ 



5. Physcosoma lurco Se). & de Man. 



Selenka, torn. cit. p. 61. 



Loc. Trengganu. 



Numerous examples. 



In the text Selenka speaks of " zwei vorderen Retractoren," 

 but in the figure he shows them as arising in the same transverse 

 line ; in these specimens the dorsal retractors arise behind the 

 ventral in the same longitudinal line, and so from the same 

 muscle-bands, namely the first and second. Moreover, according 

 to Selenka's figure, the four retractors fuse, after a short 

 course, to form two retractors, and these two, again after a 

 short course, again fuse to form one ; here, however, the four 

 retractors fuse immediately into one after a short course. 

 Further, I may mention that the anus is not necessarily con- 

 spicuous as described by Selerdca. In many cases it is quite 

 indistinguishable ; in many others it appears as a rather sunken 

 cleft-formed opening, and in only a few cases as a round opening 

 raised on a high papilla. As in the case of Sip. cunianensis, this 

 difierence of detail may be explained, w^ithout doubt, by the 

 difiering states of contraction in the various examples, either of 

 the animal as a whole or of the anal sphincter or of both. 



6. Physcosoma sociUM, sp. nov. (Plate II. fig. 1.) 

 Loc. Pulau Bidan, Penang. 



Three specimens. 



Introvert nearly half as long as the body and thickly covered, 

 especially in front, with flattened dark papilla, which posteriorly 

 become more conical, smaller, lighter in colour, and less densely 

 crowded. Those on the extreme hind end of the body are very 

 like those on the front of the introvert, but over the body 

 generally they are much more widely scattered, appearing as 

 brown spots against the paler background of the semitransparent 

 skin. These papillaj are formed of numerous concentric plates, 

 and very closely resemble those of Ph. psaron Sluiter {v. fig. 1 6). 

 There are no laooks on the introvert. The longitudinal muscles 

 number 18-21 in the middle of the body, with occasional anasto- 

 moses ; close to the postei-ior end there is a distinct convex line 

 along which they again anastomose slightly, so that behind this 

 line there are relatively fewer mixscles. The four retractors fuse 

 as soon as they meet ; the ventral pair arise just behind the 

 middle of the body from muscles 2-6, the dorsal just in front of 

 the middle of the body from the 5th-6th muscles. The contractile 

 vessel is without diverticula. The intestine has few (about 8-10) 

 spirals ; it is held to the posterior end of the body by the spindle- 

 muscle and anteriorly by two strands inserted to the left of the 

 nerve-cord ; the rectum is long and opens near the base of 

 the introvert. The nephridia are attached for two-thirds of their 

 length, which is about half that of the body; their anterior halves 

 are much swollen and their openings lie just behind the level of 

 the anus. 



