PISTA CRISTATA. 161 



The ventral scutes are about seventeen in number. Vesicles four or five small 

 terminal median scutes, and after them a median groove with a raised line continuous to 

 the posterior end. Behind and above the third and fourth bristle- tufts a smoothly rounded 

 process or long papilla occurs, and in some two are found behind the fourth. In the 

 Irish examples they are clavate. Occasionally a smaller papilla appears behind the fifth. 



In the Hebridean forms the tentacles are pale orange, the body of a uniform reddish 

 orange with a deep orange bar at each scute inferiorly. The lips are reddish, and a deep 

 red patch occurs at the anterior part of the second region. The posterior part of the 

 body is pale orange. De St. Joseph states the colour is greyish rose with pale tentacles. 



The branchia on each side arises by a long trunk in the line of the second large 

 lateral flap (third segment) and quite on the dorsum. The distal region is finely 

 branched, the whole forming a whorled arbuscle so characteristic of the genus. 

 Occasionally a third and smaller stem springs from the segment in front, and its 

 branches have the same arrangement. In an example from Shetland two large 

 branchiae of different sizes arose from the second segment, and two smaller, also of 

 different sizes, arose from the third. In some the whorled condition is conspicuous, 

 tier after tier leading to the somewhat truncate tip. It is noteworthy that the branchiae 

 cling to segments 2 and 3. 



The next segment (fourth) bears a setigerous process and a ridge but no hooks. 

 As indicated, the anterior setigerous processes are dorsal in position, but they soon 

 become lateral. Sixteen are present. Those in front and rear are less prominent 

 than the intermediate processes. The pale golden longer bristles have nearly cylindrical 

 shafts, the proximal ends being narrowed only for a short distance, and they are finely 

 striated, whilst the distal ends are curved, tapered, and soon end in a fine point, the 

 sides of the tip having well-marked wings. The tip is curved and directed dorsally 

 and posteriorly— that is, the convexity is in front. The shorter bristles have little more 

 than the tips projecting uniformly beyond the surface of the skin, and they show the 

 same form and curvature of the tip. 



The hooks commence opposite the second setigerous process — that is, the fifth 

 segment — as a single row, and the ridges leave a considerable interval between them 

 and the scutes. The rows remain uniserial till the ninth or tenth when a biserial 

 arrangement occurs to the twentieth. The hooks (Plate CXXIV, fig. 9) have a rather 

 short, stout main fang with three or four teeth above it in lateral view, and oblique 

 striae pass from these to the posterior outline of the neck. The outline below the main 

 fang is slightly angular and wide, whilst the median process on the anterior outline 

 forms a short cone with a broad base, the line then trending at a different angle 

 downward. The posterior outline is nearly straight (very slightly convex) ; then it 

 bends outward at the point of attachment of the ligament, which passes off above the 

 lower margin of the base, and thus the appearance of the hook is diagnostic. The basal 

 region is comparatively deep and has a process at its anterior and inferior angle. The 

 long ridges for the hooks cease with the bristles, and thereafter uncinigerous processes 

 project from the posterior border of each segment, the glandular tissue forming a belt 

 between them. Posteriorly the processes bear a single row of hooks. In connection 

 with the development of these hooks Hessle figures one (Plate III, fig. 3) in its capsule, 



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