422 PART II. SYSTEMATIC ACCOUNT 



379, 380; Ivanov, 1951: 739-42; Beklemishev, 1952: 289, 295-8, 386, 395, 457, 613; 

 Boettger, 1952: 292-3; Ivanov, 1952: 372-4, 388, 390; Ushakov, 1953: 179; Zenkevitch, 

 1954: 75, 77, 78; Zenkevitch, Birstein and Belyaev, 1954: 66, 68; Hartman, 1954: 183-5; 

 Ivanov, 1954b: 69-71, 79; Abrikosov et al, 1955: 472; Ivanov, 1955a: 177; Ivanov, 

 1955b: 382, 383; Ivanov, 1955c: 595; Ivanov, 1955d: 171, 176, 177; Ivanov, 1955e: 

 224; Ivanov, 1956b: 1864, 1868; Ivanov, 1956c: 165, 166, 169; Jagersten, 1956: 212, 220, 

 228, 229, 230, 233, 234, 238; Kirkegaard, 1956a: 79; Kirkegaard, 1956b: 183, 185, 186; 

 Abrikosov, 1957: 232, 233, 235; Alvarado, 1957a: 556; Beklemishev, 1957: 396, 397; 

 Ivanov, 1957a: 431, 475, 476, 478, 480, 483, 485, 490, 492, 494-8; Ivanov, 1957b: 1127, 

 1139; Beklemishev, 1958: 34, 45; Vinogradova, 1958: 112; Dajoz, 1958: 225, 226, 230-3, 

 236, 237, 238; Fell, 1958: 44-6; Ivanov, 1958a: 1363-70; Ivanov, 1958b: 1682, 1687-9; 

 Ivanov, 1960a: 1528, 1539, 1540, 1541, 1546, 1549, 1550, 1552, 1553, 1554, 1561, 1569, 

 1572, 1574, 1580, 1581, 1583, 1588, 1607, 1610, 1616, 1625; Ivanov, 1960c: 6, 8, 9, 11, 14, 

 23, 24, 26, 30, 31, 34-8, 43, 48, 56, 59, 61, 66, 67, 69, 75, 92, 97, 98, 101, 107, 115, 215, 

 227, 241-2, 252. 



Ten to 31 tentacles enter into the composition of the tentacular cylin- 

 der and the pinnules upon them are triserial. The protosoma is joined 

 to the mesosoma and the cephalic lobe to the protosoma. The pronounced 

 keels of the well-developed bridle taper strongly towards the dorsal ends. 

 The cuticular plaques of the fore-part of the trunk appear horseshoe- 

 shaped with the ends pointing backwards, and each one lies on a separate 

 pulvillus. The entire plaque consists of a thin round membrane with a 

 horseshoe-shaped thickening from which a pair of powerful apodematous 

 outgrowths penetrate into the papilla. The spermatophores are leaf-shaped 

 and broad. The tube may be smooth or segmented, with no filmy section, 

 but instead with a broad, funnel-like mouth. 



Type of the genus: Lamellisabella zachsi Ushakov. 



There are four known species: Lamellisabella zachsi, L. johanssoni, L. 

 ivanovi and L. minuta. 



Key for determining the species of Lamellisabella 



1 (2) The ventral ends of the keels of the bridle are fused together. The 



keels possess prominent crests and are not less than 120/a broad. 

 There are 18 tentacles. The transverse horseshoe-shaped plaques 

 are с 70/a across. The girdles of toothed platelets are interrupted 

 dorsally. The tube is segmented. 2. L. johanssoni Ivanov (p. 429). 



2 (1) The ventral ends of the keels of the bridle are not fused, the keels 



have no sharp crests and are considerably less than 120/x broad. 



3 (4) There are ten tentacles. The mesosoma is less than 0-5 mm in 



diameter. The keels of the bridle each consist of a thin colourless 

 cuticular axis and an attached brown band which breaks up into a 



