SIBOGLINUM WEBERI 181 



the metameric region of the trunk. The ventral papillae of the 

 postannular region carry hoop-shaped cuticular plaques. The thick- 

 walled tube has complete, or partially incomplete, short brownish 

 grey rings, sometimes anastomosing with one another. 



24. S. atlanticum (p. 263). 



47 (42) Pinnules are absent. A post-tentacular groove runs at the very base 



of the tentacle. A narrow glandular girdle, interrupted dorsally and 

 ventrally, lies behind the bridle. Many small papillae are randomly 

 placed in the zone of thickened papillae. The toothed platelets, 

 11-12/u, long, are arranged in a single row in each of two widely 

 separated girdles. The tube has long rings, some of them blotched 

 or consisting of two or three secondary rings. 



19. S. bogorovi (p. 244). 



48 (41) The mesosoma lacks any glandular region of integument. There is 



a post-tentacular groove. The toothed platelets, 16-19/x long and 

 shaped like the sole of a shoe, are arranged in three girdles, of which 

 the front two lie close together, some distance from the hindmost. 

 The delicate transparent tube has very short brownish rings looking 

 like barrel hoops. 22. S. robustum (p. 254). 



1. Siboglinum weberi Caullery (Figs. 1^4, 96) 



Caullery, 1914: 2014, Figs. 1-6; Caullery, 1944: 1-26, Figs. 1-89; Caullery, 1948 

 495-9, Figs. 117-20; Dawydoff, 1948: 141-63, Figs. 1-12; Ivanov, 1951: 742; Ivanov 

 1952: 372; Zenkevitch, 1954: 77, Fig. 9; Zenkevitch, Birstein and Belyaev, 1954: 66, 68 

 Fig. 10; Ivanov, 1954b: 69; Hartmann, 1954: 184, 185; Ivanov, 1956b: 1863; Jagersten 

 1956: 212, 227, 230, 231; Kirkegaard, 1956a: 79, 82; Kirkegaard, 1956b: 186, Fig. 4 

 Abrikosov, 1957: 232, 233, 236, 238, Fig. 1; Ivanov, 1957a: 431, 444, 458, 459, 491, 494 

 Ivanov, 1957b: 1127; Borradaile et al., 1958: 714-16; Vinogradova, 1958: 112; Dajoz 

 1958: 225, 234, 237, Fig. 6; Ivanov, 1958a: 1363; Ivanov, 1958b: 1682, 1689, 1690 

 Ivanov, 1958d: 1; Ivanov, 1958e: 1070; Ivanov, 1960a: 1524, 1525, 1529, 1531, 1549, 1559 

 1562, 1567, 1592, 1606, 1607, 1611, Fig. 1436; Ivanov, 1960c: 5, 7, 12, 14, 35, 46, 50, 54 

 92, 93, 96, 125, 126, 128, 129-31, 136, 145, 158, 265, Figs. 1, 56, 87, 96; Southward, 1961 



2, 3-5, 21, Fig. 1 (revised description). 



To all appearances, the various peculiarities mentioned by Caullery in his 

 description of S. weberi belong to at least two different species, whose diag- 

 nosis is not at present possible. The form of the anterior division of the body, 

 for instance, and the relative proportions of its parts, vary in different indi- 

 viduals to an extent that is difficult to explain as mere differences of degree 

 of shrinkage upon fixation (Caullery, 1944; Figs. 6, 9). Some specimens, to 

 all appearances, have distinct glandular belts on the mesosoma (Caullery's 



