394 PART II. SYSTEMATIC ACCOUNT 



2 (1) There are not less than 26 tentacles, often many more. The fore-part 



of the body is not less than 2-5 mm long. 



3 (4) There are between 26 and 39 tentacles. The mesosoma bears three 



secondary transverse grooves in front of the bridle, whose keels are 

 black, with thickened ventral ends which meet. The fore-part of the 

 body is c. 3 mm long, and less than 1 mm broad. 



1. P. annulata (p. 394). 



4 (3) There are about 70 tentacles, and two secondary grooves on the meso- 



soma in front of the bridle whose keels are thin and delicate and do 

 not meet ventrally. The fore-part of the body is c. 4 mm and more 

 than 1 mm broad. 2. P. barbata (p. 398). 



1. Polybrachia annulata Ivanov (Figs. 7, 11, 13, 17C, 156-8) 



Ivanov, 1952: 379-382, 389, Figs. 13-18; Zenkevitch, 1954: 77, Figs. 6, 9; Zenkevitch, 

 Birstein and Belyaev, 1954: 68, Figs. 9, 10; Hartman, 1954: 185; Ivanov, 1954b: 73, 77, 

 Figs. 4, 8; Ivanov, 1955e: 224, PI. 65, Fig. 4; Jagersten, 1956: 238; Kirkegaard, 1956b: 

 185, 186, Fig. 4; Ivanov, 1957a: 442, 449, 481, 490, 492-7, Fig. 59; Ivanov, 1957b: 1139; 

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

 Ivanov, 1958a: 1363, 1369, Figs. 11, 12; Ivanov, 1958b: 1682, 1687, 1689, Figs, 2, 5, 6; 

 Ivanov, 1958e: 1078, 1079; Southward, 1959: 443; Ivanov, 1960a: 1534, 1538, 1540, 1541, 

 1558, 1565, 1606, 1608, 1609, 1612, 1613, Figs. 1389, 1393, 1399, 1410, 1416-17, 1429, 

 1437, 1449-50, 1465; Ivanov, 1960c: 6, 12, 22, 23, 25, 27, 51, 76, 92, 94, 96, 167, 231-5, 

 237, 240, 250, 266, Figs. 7, 11, 13, 17, 29, 35, 36, 40, 49, 57, 68-9, 845, 87, 156-8. 



In front of the bridle the mesosoma is ringed with three secondary grooves 

 (Fig. \%A). The cephalic lobe is an equilateral triangle with gently rounded 

 corners and it is divided from the protosoma by a transverse groove, most 

 noticeable on the dorsal side (Fig. 1565, C). A deep, mid-ventral furrow on 

 the mesosoma in front of the bridle cuts across the secondary rings, while 

 behind the bridle stretches a cutaneous ridge which gradually broadens 

 towards the hind end of the mesosoma. The tentacles vary in number from 

 26 to 39, forming a very long crown (Fig. 7) whose base is a horseshoe, 

 opening towards the ventral side (Fig. 156^4). In the dorsal part of the crown 

 the tentacles are arranged in two rows, laterally they form three rows, while 

 on the ventral side only one row (Fig. 17C). The numerous pinnules form 

 four to five dense rows on each tentacle. 



The metameric division of the front part of the trunk is about two or three 

 times as long as the whole fore-part of the body and accounts for about a 

 tenth of the overall length of the preannular region. The ventral sulcus, dis- 

 tinguished by its considerable breadth (Fig. 156.4), is bounded by rather 



