250 PART II. SYSTEMATIC ACCOUNT 



(Fig. 124C). Behind the bridle, on the dorsal side of the mesosoma, a pair of 

 long, triangular bundles of longitudinal muscle fibres may be made out, under 

 the skin (Fig. 124$). The hind edge of the mesosoma is arched backwards on 

 the dorsal side and slightly concave ventrally. 



The anterior metameric portion of the trunk is somewhat less flattened 

 dorso-ventrally than the mesosoma. The ventral sulcus is bounded by com- 

 paratively large, elongated papillae, devoid of plaques (Fig. 124.4). The front 

 end of the well-developed dorsal ciliated band is wider than farther back 

 (Fig. 1245). The middle nonmetameric part of the trunk bears scattered 

 pointed lateral glandular papillae (Fig. 124D), while in the mid-ventral line, 

 in the zone of thickened papillae, lies a single row of five transparent, conical 

 papillae, placed close together, one behind the other, each bearing on the 

 tip a noticeable thickening of the cuticle (Fig. 124E). The two girdles of the 

 metasoma lie close together on muscular ridges (Fig. \24F). The uniserial 

 colourless toothed platelets are narrow at the front end and lack the anterior 

 group of teeth (Fig. 124G). They are 10—1 1/u. long. The very long, slender 

 postannular region of the trunk is furnished with metameric button-like 

 dorsal glandular shields, but is devoid of papillae (Fig. 124Я). 



The parts of the body have the following dimensions : length of the tentacle, 

 c. 4-5 mm; length of the anterior section of the body, 0-35-0-45 mm; 

 breadth of the mesosoma, 0-1 mm; overall length of the body, including the 

 tentacle, 50-55 mm. 



The cigar-shaped spermatophores taper evenly towards both ends, and 

 the filament has an expanded base (Fig. 125Л). They are about 0-11 mm 

 long. 



The unsegmented tube, rather dark red-brown in colour, possesses very 

 stout walls, as may easily be seen in optical section (Fig. 125$). It consists of 

 irregular rings of a dark material, with narrow, clear intervals between them. 

 In the hind part of the tube the rings are very much shorter and the intervals 

 between them correspondingly longer, and often constricted or pinched in 

 (Fig. 125C). The material of the tube is very hard and brittle. The longest 

 fragments reach 15 cm in length and 0-1-0-12 mm in diameter. The trans- 

 parent ringless front part of the tube is not less than 1-5 cm long, and the 

 hindmost part, also unringed and transparent, reaches 1 cm in length. The 

 tube tapers very little, losing only 10/a in diameter for each 4 cm, i.e. a taper 

 of 2-5/x/cm. 



5. minutum is sharply distinguished from all other species by the small 

 protosoma, with its pair of lateral swellings. Not less characteristic are the 

 following features : the very small, conical, cephalic lobe, the peculiar nature 



