POMATOCERUS TRIQUETER. 367 
The body (Plate CXVII, fig. 1) is widest anteriorly, where the alar membrane further 
increases the breadth, and tapers gradually to the tail, which ends in a somewhat broad 
tip, with a papilla at each side. The dorsum anteriorly is pale brown or purplish-brown, 
whilst the general colour posteriorly is dull yellow with pink lateral regions. It is rounded 
dorsally, shghtly flattened and grooved ventrally. The anterior region consists of six bristled 
segments’ and the fused peristomial segment, thus differmg from Serpula and Hydroides in 
the absence of the conspicuous first pair of bristles on the dorsal edge of the fused collar 
and alar membrane. The alar membrane passes backward above the bristles, the sides 
separating as they go to fuse with each other as a broad thin flap on the ventral surface 
behind the anterior region. Anteriorly it and the collar are yellowish externally and bluish 
internally, and the same bluish colour appears laterally and posteriorly. The posterior 
region has sixty to seventy segments. The two papille below the anus are rounded 
distally with a broad stall proximally, but vary with the movements of the vent in 
its respiratory functions. All the bristles are directed upward and backward as pale 
golden flattened tufts, and the structure is the same throughout this region. Hach 
bristle (Plate CXXXI, figs. 7 and 7a) has a translucent and nearly cylindrical shaft, 
with a slight curvature toward the commencement of the tapering tip, which has two 
narrow wings so arranged that in certain views the space between them seems to be 
hollowed out. 
The posterior bristles (Plate CX XXI, figs. 75 and 7b’) have slender, cylindrical shafts, 
which diminish and then dilate superiorly as they approach the broad shoulder, the spinous 
distal edge of which has a concavity trending on one side to a delicately tapered whip. ‘This 
peculiar tip would seem to combine the functions of the long simple and the brush-shaped 
bristles of other forms. 
The anterior bristles have a proportionally short hold of the tissues—a feature of import- 
ance in connection with the habits of the annelid, and whilst they pomt upward and back- 
ward, the posterior are directed transversely or ventrally and slightly forward. In each 
case the bristles are at the end of the rows of hooks—the anterior at the dorsal end, and the 
posterior at the ventral end. 
The alimentary canal appears to be similar to that of Sabella—iorming a moniliform 
duct—wide anteriorly and diminishing posteriorly. It is coated with nucleated cells 
externally. 
The ccelomic corpuscles are large and round. De St. Joseph found Protozoa 
apparently teferable to Anoplophyra, Stein, in the intestine. A yellowish coiled gland 
occurs anteriorly—external to the gut and adhering to the body-wall. Its structure is 
granular. 
The anterior hooks (Plate CX-XXI, fig. 7c) have the shape of a triangle, the posterior 
outline (slightly concave) gently curving to the crown and forming the base of the triangle, 
the sides of which are formed by the anterior outline with its eight teeth and the peculiarly 
modified main fang, which resembles a blunt probe-like process with a small incurvation 
beneath, the prow being minute and trending with a slight curve to the inferior outline, 
which is nearly straight, and the body of the hook is crossed by oblique strize. The number 
1 De St. Joseph states that there are seven, but six only occur in Britain. 
