266 PART II. SYSTEMATIC ACCOUNT 



girdle lying behind them. In this same specimen a characteristic group of 

 four ventral cone-shaped papillae lay in front of the girdle (Fig. 13 \E). The 

 toothed platelets, which lie in three or four rows (Fig. \3\F), are rather broad, 

 slightly narrower, in the front third, and rounded at the ends. The well- 

 developed front group of teeth occupies about a quarter of the surface of each 

 platelet, and is considerably less in area than the better developed hind group. 

 The platelets are 14-18/x long by 4-6/x broad. Southward and Southward did 

 not describe the toothed platelets, contenting themselves with a figure, which 

 did not show the anterior teeth. The postannular region of the trunk is long 

 and slender and the metameric glandular shields well developed but irregu- 

 larly shaped. Each consists of four to six or more, densely packed, rounded 

 protuberances, in each of which lies a single pyriform gland, while the tip of 

 each protuberance is marked by the aperture of the gland (Fig. \3\H, I). 

 The large conical ventral papilla lying opposite each dorsal shield widens out 

 transversely towards the base and is invariably furnished with rather coarse, 

 curved or rod-shaped brownish cuticular plaques, up to 40-60//. across. 

 Occasionally, to judge by my one specimen, on each side of the papillae 

 smaller supplementary papillae are sometimes developed, also bearing 

 cuticular plaques (Fig. 1317). In a sense these form the rudiments of a trans- 

 verse row of papillae, very reminiscent of the metameric postannular rows of 

 papillae in the Thecanephria. 



According to the data given by Southward and Southward the dimensions 

 of the parts of the body are as follows: length of the tentacle, 20 mm; length 

 of the protosoma, 0-68-0-87 mm; length and breadth of the mesosoma, 

 2-5-2-9 mm and c. 0-36 mm, respectively; length of the metameric part of the 

 preannular region, 15-20 mm; length of the nonmetameric part of the trunk, 

 c. 50-60 mm, of which the distance between the front edge of the zone of 

 thickened papillae and the girdles accounts for 8 mm and the length of the 

 postannular section for 28 mm; overall length of the body, excluding the 

 tentacle, 112 mm. 



The spermatophores (Fig. A131) are very long and narrow, pointed at 

 both ends, and measure 500/x x 30/*. 



0.1мм 

 I 



Fig. A131. Siboglinum atlanticum : spermatophore. (E. C. Southward.) 



