SIBOGLINUM BOGOROVI 245 



five to six times as long as broad (Fig. 123Д B), and possesses a distinct 

 annular groove behind the base of the tentacle. The conical cephalic lobe is 

 not large and the long rather slender tentacle has no pinnules. The delicate 

 keels of the bridle, which is situated in the front part of the mesosoma, are not 

 fused ventrally and nowhere near meet dorsally, but are situated on slightly 

 raised cutaneous ridges. Weakly developed lateral glandular regions are 

 found behind the bridle (Fig. 123Д B). The hind edge of the mesosoma is 

 slightly concave on both dorsal and ventral sides. 



The rather long, metameric part of the preannular region of the trunk has 

 small rounded papillae, each showing the dark pore of a pyriform gland 

 (Fig. 1235). In the hind part of the metameric region the papillae become 

 larger and their arrangement somewhat irregular (Fig. 123C). In one indi- 

 vidual in which they were counted there were 53 on the left side and 63 

 on the right. The ventral sulcus of the metasoma is rather wide (Fig. 1235, C), 

 and the dorsal ciliated band in no way remarkable (Fig. 123A). In the zone of 

 thickened papillae there are about 20 comparatively large, higgledy-piggledy 

 papillae on the ventral side (Fig. 123Z)), but these do not bear cuticular 

 plaques. In this species, as in so many others, there are two girdles of toothed 

 platelets, but they are unusual in being situated rather far apart, lying on 

 muscular ridges. Each consists of two halves, which are separated by a wide 

 gap ventrally, while dorsally they meet (Fig. 123£, F). Behind the second 

 girdle lies a large ventral finger-shaped papilla (Fig. \23E). The uniserial, 

 yellowish toothed platelets (Fig. 123G) are very characteristic, with the front 

 end only half as wide as the back part. The surface of each platelet is covered 

 with comparatively large, sharp teeth, of which the first group, with teeth 

 pointing backwards, is quite well developed but only occupies a half to one- 

 third the area of the hind group (Fig. 123//). The platelets are about 1 1— 12/x 

 long, 5ju. wide at the back and 2-3/x near the front. The very long postannular 

 section of the trunk is furnished with more or less metameric small, dorsal, 

 glandular shields, shaped like dumb-bells draped across the width of the 

 trunk. In each of the lateral expansions of the shields may be seen the duct 

 of a pyriform gland, from which it may be inferred that there is a pair of 

 glands in each shield. Opposite each shield lies a conical ventral papilla with 

 a small cuticular thickening at the tip. The postannular region bears in 

 addition numerous small scattered wart-like glandular papillae. 



A typical individual of S. bogorovi has the following dimensions: length of 

 the tentacle, 5 mm; the anterior section of the body, 0-8 x 0-14 mm; 

 breadth of the body at the level of the girdles, 0-15 mm; distance between the 

 girdles, 0-9 mm; overall length of the body, с 25 mm. 



