656 Memoirs of the Indian Museum. [Vol,. V, 



Gunn., or Pomatoceros triqueter, L. When free or erect the tube is circular in section, 

 with a single dorsal ridge, which is usually worn away in the older part of the tube 

 (fig. 27M, a and b). The ridge terminates over the orifice in a small sharp tooth. 

 Where the tube is attached, it tends to flatten on the ventral surface, and spreads 

 out two later o- ventral ridges (fig. 27M, c). This flattening of the attached tube is 

 due to the thickening of the walls in the latero- ventral region, the bore remaining 

 almost circular in section. 



A rather elongate specimen is 11 mm. in length, of which the abdomen is 8 mm., 

 the thorax 2 mm., and the branchiae -5-1 mm. The width of the body is '5-75 mm. 

 The thorax is composed of 7 setigerous segments, the abdomen of 43-57 segments 

 and in addition there are 6 or 7 narrow rings forming the tapering posterior end. 



The specimens are all stained a deep reddish brown by pigment extracted by the 

 preservative spirit from the wood to which they are attached, and the original colour 

 pattern is obscured. Traces of deep blue pigment bands remain on the branchiae 

 and thorax, and other pigment is present, so that probably the living animals were 

 coloured rather after the manner of Pomatoceros triqueter, L- 



The branchiae are 13-17 in number, 7-9 on the right side, 6-8 on the left. In 

 addition, the left dorsal branchia forms the operculum. Each branchia has 3-5 

 diffuse bands of dark pigment, which spread on to the adjacent filaments. There are 

 18-20 pairs of rather long filaments on each branchia. The naked tip varies greatly 

 in length, and may be longer or shorter than the filaments. The longest filaments 

 are attached just above the middle of the stem, and those at each end are shortest. 

 The stem of the branchia bears no other appendages. 



The operculum usually exceeds the branchiae in length. The stem is rather 

 flattened (figs. 27A, 27c), and passes more or less abruptly into the swollen head. 

 The latter varies in shape according to the manner in which it is compressed within 

 the tube, the two extreme forms being shown in figs. 27A and 27c. It is rather fig- 

 shaped, and tends to spread out over the branchiae, so as to protect them when 

 withdrawn into the tube. The distal end is almost flat in some specimens, as in fig. 

 27c, in others it is markedly convex. There are no outgrowths either on the stem 

 or the head of the operculum. Usually there are patches of pigment, a narrow band 

 just beneath the swollen head being rather constant. 



The thorax (fig. 27A) is composed of 7 setigerous segments. The free margin of 

 the thoracic membrane is entire, except for adventitious lobes. 



The ist setigerous segment bears dorsal bundles only. They are much nearer 

 the mid-dorsal line than those of the succeeding segments, and are lodged in small 

 depressions, the setae being directed forwards. There are two kinds of setae in 

 these bundles. The stouter kind, usually 3 in a bundle (figs. 27D, 27E), have very 

 slender tips, with a series of very coarse teeth, diminishing in size towards the smooth 

 tip. For some distance beneath these teeth the shaft is smooth. Then comes a 

 transverse row of teeth, varying in number, but there is always present a large 

 median tooth, with a smaller one on each side. In addition there are usually 2-4 

 smaller teeth on each side, but sometimes these are indistinct. These setae are 



