ARWIDSSONIA ZETLANDICA. 333 



slightly narrower ridge, which ceases at the enlargement of the keel in front, but springs 

 from the side of the keel in front of the posterior rounded area. A deep groove lies 

 between the keel and the lateral ridge, and another less pronounced to the exterior of it. 

 The former probably represents the nuchal groove, which debouches anteriorly on each 

 side of the minute frontal process. The groove outside the ridge runs forward in the 

 same direction, but appears to have a less definite termination. The proboscis (Plate 

 XCIX, fig. 6 a) forms a somewhat globular, grooved mass, with rows of rather long, conical 

 papillae (Plate XCIX, fig. 6 b). 



The body is, as usual, narrowed behind the anterior end, and again increases at the 

 eighth segment. Anteriorly the feet arise nearer the anterior than the posterior border 

 of the segment, but posteriorly they are close to the posterior edge. The number of 

 bristled segments is uncertain. The last setigerous process and row of hooks are followed 

 by three narrow, non-bristled segments, bearing rudimentary homologues of the feet in the 

 shape of glandular enlargements, the last forming the prominent ring (Arwidsson's callus- 

 ring) from which the caudal funnel projects. On the ventral surface a ridge runs from 

 the first bristled segment to the edge of the caudal funnel. The body does not diminish 

 much posteriorly, and has a broad, circular shelf in front of the funnel (Plate XCIX, 

 figs. 6 e and 6f), from which it projects like a fluted vase— that is, has a constriction 

 immediately above the base and then gradually dilates to the rim bearing the cirri, 

 which, like those of Axiothella catenala, are more or less alternately long and short, 

 one of the longer occurring in the mid-ventral line or close to it. The grooved condition 

 of the funnel is a prominent feature, three cirri generally being included in each space, 

 though a narrow one may have only two. One had forty-four flattened cirri, of which 

 twenty were long. The anal cone forms a rounded button at the base of the vase, with 

 the central (anal) aperture surrounded by minute papillae. 



In contrast with Axiothella catenala the anterior bristled segments are more glandular, 

 segments 1 to 8 showing glandular rings, especially anteriorly. The bristles of this 

 region also are more prominent than in the other species. 



The first three bristled segments bear spines, the first having two or three and the 

 second and third four of the same character. The spines (Plate CX, fig. 5 b and 5 c) are 

 curved at the strong point and the shaft is striated internally up to the tip. The spines of 

 the third segment are longer. The fourth segment has a considerable row of hooks 

 (about twelve) with long, curved shafts, and a well-marked shoulder from which the neck 

 dilates to the crown. The main fang arises nearly at a right angle to the neck and is 

 rather long. Four teeth occur on the crown behind it, and a short tuft of gular bristles 

 springs from the throat immediately beneath it. They do not reach the tip of the great 

 fang. The crowns of these hooks are little elevated, and thus differ from the typical forms, 

 which those of the fifth foot more nearly resemble. The bristles form conspicuous, pale 

 yellow tufts in each foot, and one group has stout shafts and tapered tips with wings 

 (Plate CX, figs. 5 and 5 a), the others are translucent, slender, with greatly elongated hair- 

 like tips and extremely minute serrations, the wings being slightly developed. In the 

 middle and posterior regions of the body they are borne on long, setigerous processes, 

 which form a feature in the outline. They may be contrasted with those of Axiothella 

 catenala from the Arctic seas in Plate CX, fig. 4 



