TETRERES MURATA. 11 



the bristles become more prominent and longer, the uncinigerous flap projects more 

 laterally than ventrally, and the region of the conical cirrus becomes a flattened ridge with 

 a small papilla ventrally — behind the prominent setigerous process. The ventral bristles 

 are in front directed obliquely inward and forward, but as they become longer and more 

 slender posteriorly they have a tendency to slope outward and forward, and lastly, in front 

 of the caudal process, the long silky hairs are directed backward, as, indeed, Dr. Allen's 

 figure indicates. 



In structure the ventral bristles (Plate CXIII, fig. 1 e) have long smooth shafts with 

 whorls of spikes on the tip, which is extremely attenuate. Moreover, in glancing at the 

 fascicles it is apparent that two series of bristles are present, viz., the stronger kind just 

 described, and a less robust series which are finely tapered and quite smooth. All have 

 tapered bases with the fillet at the tip, and the shafts are translucent. The same structure 

 preA^ails in those immediately in front of the caudal process, the whorls of spikes being 

 very distinct, but the smooth bristles have now attained pre-eminence, and their finely 

 tapered extremities stretch far beyond those with the whorls of spikes. 



The branchiae are twenty-one in number, including the rudimentary forms posteriorly, 

 and are of a deep brown colour. The first is smaller than the second and has only a single 

 frill. The second is flattened and has a double frill — that is, one along each edge. Those 

 following have a single frill situated along the anterior and inner border. They reach their 

 maximum size about the seventh or eighth segment of the third (abdominal) region, and 

 thereafter diminish in bulk, the frill disappearing in three or four of the more slender 

 terminal branchiaa. 



The hooks, which form dense rows on the edges of the lamellse, have an elongated 

 form (PI. CXXIII, fig. 1/), the posterior outline being almost straight, a very slight 

 convexity occurring in the middle. In the anterior hooks the crown is rounded, the outline 

 being broken only by the slight notch for the attachment of the tendon. As a rule 

 six recurved teeth are present, though a minute additional one is often seen at the crown. 

 The prow is somewhat narrower than the crown and is also more or less rounded ; minute 

 incurvations for the attachment of the two tendons, however, occur. On the other hand the 

 posterior hooks (Plate CXXIII,. fig. 1 g) have a distinctly concave posterior outline and a 

 more convex anterior edge usually with eight recurved teeth, the crown and base being 

 similar to those in front. 



The caudal appendix shows four or five transverse ridges and papillaa on each side at 

 its commencement ventrally, as if such indicated a continuation of segments. On the 

 dorsal surface rings only occur (Plate CXVIII, fig. 1). 



The tubes (Plate CXVIII, fig. 1 d) are built of two layers, an internal layer of 

 comparatively small pieces of shell or thin, flat stones, arranged with considerable regu- 

 larity and forming a smooth internal surface, and an external layer of large pieces of 

 gravel and shell forming a strong but rugged and irregular outer covering (Allen). 

 Arnold Watson has found that the animals are social with gregarious tubes, " which are 

 as smooth externally as can be expected since they are composed chiefly of small shells 

 or other fragments attached by the flat surface, with here and there a larger shell at long 

 intervals. Most of the pieces are evidently from the middle of the tube, both ends being 

 absent, but the outer ends of the tubes are only half as thick as these, the diameter is 



