The Genus Synchaeta. By C. F. Rousselet. 409 



The body is more cylindrical in shape than the other species 

 of the genus, rounding off towards the foot, which is very flexible 

 and distinctly marked off, narrow, fairly long, and terminated by 

 two small pointed toes always carried well apart. The auricles are 

 powerful, but less broad than in some other species ; the head is 

 prominently pointed in front, and carries the usual pair of style- 

 like antenna? issuing out of a triangular flap of the integument, 

 and two small styles on the dorsal frontal edge of the head. 

 Below the frontal eye, exactly in the middle of the front and 

 above the mouth, this species has a large tubular antenna of 

 peculiar structure, not known, so far, in any other species of Syn- 

 chaeta. It consists of a bundle of fine setae protruding out of a 

 fairly long, fleshy tubule pointing straight forward. The usual 

 median dorsal antenna above the eye is also present. The mouth 

 is situated immediately below the pointed front, is surrounded by 

 the usual four tufts of stiff setae and four patches of vibratile cilia. 

 The mouth-opening itself is V-shaped and, as in all other species, 

 is guarded by a single row all round of closely set, short, stiff hairs, 

 all converging over its centre. The lateral antennae are very small, 

 and situated in the lumbar region, about two-thirds down the side 

 of the body, and slightly on the ventral side. The median eye is 

 large, deep red in colour, looking like two eyes closely apposed. 

 The mastax is large and of usual Synchceta tremula type with some 

 variation in the shape of the rami (fig. 19c) ; the unci have one 

 large tooth and four or five very small teeth, mere serrations 

 (fig. 196). The large stomach, intestine, lateral canals, and con- 

 tractile vesicle are of usual structure and call for no particular 

 remark. The ovary is large and roughly oval in shape. The eggs 

 are not carried about, and I have seen an egg lying beside the ovary 

 with a rather stout, smooth shell, measuring 11*5 ^ by 9*5 jx. 



This species swims with such impetuosity through the water 

 that its rush cannot be described otherwise than furious ; its course 

 is straight forward, then it dashes suddenly round in another direc- 

 tion, lashing its foot up and down and right and left, attacking any 

 other Synchaeta that may come in its way, and not at all particular 

 as to species. I have seen it seize an unfortunate S. triophthalma 

 with its jaws, carry it in its mouth and devour it without a moment's 

 stop in its furious career. 



No other Synchaeta of my acquaintance is so fast in motion 

 and so fierce of temper. In this respect it can only be compared 

 with Plocsoma hudsoni, which is equally wild and fierce. 



In retraction the auricles are turned in over the head, and a 

 fold of the skin closes over them, while the foot is completely re- 

 tracted within the body. 



The male. The Synchaeta males are rare, but I observed the 

 male of this species attached to the posterior part of a large 

 female, while at the same time the latter was rushing through 



August 20th, 1902 2 e 



