ODONTOSYLLIS GIBBA. 185 



In the example from Plymouth the colouration consists of numerous isolated brownish 

 specks (Plate XLIX, fig. 4) which here and there form a band. 



A figure of the proboscis is given by Marion and Bobretzky, showing a series of 

 denticulate papillaB anteriorly. 



The foot (Plate LXX, fig. 13) is uniramous in so far as there is only one spine. The 

 dorsal moiety of the foot, however, may be held to be represented by the elevated region 

 at each side from which the dorsal cirrus springs. The cirrus is clavate — somewhat like 

 that of Lepidonotus — with a dilated region towards the tip, followed by a slender 

 terminal process. The anterior cirri have the largest dilatations, the posterior being 

 more slender, though still rendered characteristic by the white ring towards the tip. The 

 setigerous region is separated from the foregoing by a marked sulcus, the dorsal margin 

 of the lobe being convex, and it terminates externally in two short conical papillae, while 

 beneath the lobe is a larger conical process, which may represent the ventral cirrus, 

 unless that is altogether absent. It does not extend quite so far outward as the upper papillge. 

 The bristles (Plate LXXIX, fig. 7) have a long, slender, translucent shaft, curved towards 

 the dilated distal end where it has a shoulder and a bevelled edge. From the shoulder 

 passes off the terminal blade, which is short, very slightly diminished at the tip, and ends 

 in a simple hook, a feature not clearly indicated by Marion and Bobretzky. The bristles 

 form a diminishing series from above downward both as regards the length of the shaft 

 and the terminal pieces. The ventral cirrus forms an elongated conical process. 



This species is Hesione-like in its active movements and irritability. When at rest the 

 anterior six segments of the body are elevated. Marion and Bobretzky's examples swam 

 freely to and fro like Nereids. It differs from the form described by Claparede and Marion 

 and Bobretzky in the arrangement of the eyes, the anterior and posterior pairs of which 

 are more widely separated ; and still more in the shape of the dorsal cirri, which instead 

 of forming fusiform or gently clavate organs are somewhat cylindrical with a rather 

 sudden bulbous dilatation distally, from which a slender filiform tip projects. On the 

 whole, however, in the present state of our knowledge it will suffice to indicate the variety, 

 especially as the bristles do not appear to differ materially in structure. 



A similar form (young?) comes from the tow-net in St. Andrews Bay, 1894. The 

 setigerous process of the foot seems to differ slightly in its relation to the ventral cirrus, 

 but this may be due to youth. 



Claparede and Grrube described and figured this form within the same year, and it 

 appears to be extensively distributed. 



Malaquin 1 (1893) observes that the protoplasmic " setting " of the muscular fibres of 

 the proventriculus has totally disappeared, only the longitudinal fibrils of the column 

 being present. Each column has transverse striation as in Syllis hyalina. 



So far as can be made out the Umbellisyllis fasciata of M. Sars 2 appears to be this 

 species, though the large size (24 mm.) gives a margin for variation, and the presence of 

 an additional minute pigment-speck in front of the anterior pair is novel. Whatever 

 may be the condition as regards specific identity, the Norwegian form is an Odontosyllis 

 from deep water — viz., 100 to 300 fathoms. 

 1 Op. cit., p. 231. 



3 ' On some Remarkable Forms of Animal Life, etc./ 1872, p. 41, pi. iv, figs. 12 — 18. 



81 



