398 PART II. SYSTEMATIC ACCOUNT 



a few of which may run together to form more or less complete rings 

 (Fig. 1585). 



P. annulata is distinguished from other species by the possession of three 

 secondary grooves on the mesosoma and by the solid coarse keels of the 

 bridle. In the number of tentacles this species occupies an intermediate 

 position between P. gorbunovi and P. barbata. 



Material : many tubes, some with animals. 



Localities : P. annulata is encountered both in the abyssal zone of the Sea 

 of Okhotsk, where it occurs together with Lamellisabella zachsi, and in the 

 abyss of the southwestern part of the Bering Sea, of which it is especially 

 characteristic. 



Depth: 1440-5000 m. 



2. Polybrachia barbata Ivanov (Figs. 172), 159) 



Ivanov, 1952: 383-4, 388, 389, Figs. 19-22; Zenkevitch, 1954: 78, 80, Figs. 7, 9; 

 Zenkevitch, Birstein and Belyaev, 1954: 68, Fig. 10;Hartman, 1954: 185; Ivanov, 1954b 

 74, 77, Fig. 5; Ivanov, 1955e: 224, PI. LXV, Fig. 5; Jagersten, 1956: 238; Kirkegaard 

 1956b: 186, Fig. 4; Abrikosov, 1957: 234, Fig. 4; Ivanov, 1957a: 492, 496, Fig. 59 

 Vinogradova, 1958: 112; Dajoz, 1958: 233, 236, 237, Figs. 2 (incorrectly labelled), 6 

 Ivanov, 1960a: 1530, 1539, Fig. 1399D; Ivanov, 1960c: 6, 12, 231,235-7, Figs. 17,87, 159. 



Two transverse secondary grooves, which cross the mesosoma in front of 

 the bridle (Fig. \S9A, B), are intersected by a rather broad mid-ventral 

 furrow which is very broad at the front and, in contrast with the analogous 

 furrow in P. annulata, does not reach back as far as the bridle. The cephalic 

 lobe is like that of P. annulata, with a blunt tip and delimited behind by a 

 transverse groove (Fig. 159 A). The tentacles are very long and numerous, 

 numbering 71 in the only known specimen. The surface to which they are 

 attached is shaped like a horse-shoe with incurved ends and the base of the 

 tentacular crown covers the whole area of this horse-shoe, with the tentacles 

 arranged in several rows (Fig. \1D). The very delicate, slender keels of the 

 bridle, which lie on low ridges (Fig. \59A, B), do not run close to each other 

 either dorsally or ventrally. The back end of the mesosoma is slightly com- 

 pressed dorso-ventrally and ends in two small dorsal protuberances. 



The ventral sulcus of the metameric part of the trunk is broad (Fig. 1595) 

 and the dorsal ciliated band is well developed. The whole of the remainder of 

 the preannular part and the entire postannular region remain unknown. The 

 small oval cuticular plaques of P. barbata are interesting in that many of 

 them are clearly double, consisting of two in tandem (Fig. 159C). The front 

 plaque of such a pair is always well developed, the posterior plaque sometimes 



