AMPHICTEXE AURICOMA. 47 



these are the bristles with the spear-shaped enlargement and the finely-tapered tips, 

 the shafts being also robust. The posterior bristles are considerably smaller, but 

 they keep to the same type, those with the spear-shaped tips being proportionally 

 longer. 



The caudal hooks are situated on each side of a small keel (notched at its free end) 

 which marks the median dorsal region of the caudal appendage. They are distinguished 

 by their comparatively great length and straightness, by the rapid diminution at the 

 neck, and by the abrupt curve and sharp condition of the hook at the tip (Plate CXXIV, 

 fig. 2 b). The edge of the process is deeply and symmetrically notched, usually curved 

 ventrally, and the dorsal lip of the vent is prolonged as a somewhat flattened conical 

 process with a dorsal papilla on its surface which curves beyond the split ventral lip. 

 The dorsal surface of the process is concave, forming a deep groove, whilst the ventral 

 is convex and grooved by oblique furrows, directed outward and backward. It seems to 

 be easily regenerated, even before the bristled segments necessary to complete the series 

 are formed, and thus some examples are peculiarly short and broad, the tapered posterior 

 region of the body not yet having been reproduced, whilst the caudal process is fully 

 developed. 



The lamellar hooks (Plate CXXIV, fig. 2 c) have six teeth from the crown down- 

 ward ; then follows a finely spinous process (like a large tooth with serrations), below 

 which is a notch directed upward, and lastly the rounded prow which is nearly in a line 

 with the face of the hook. The shaft is short and comparatively broad. The finely 

 serrated part above the prow is slightly longer proportionally than in Pectinaria belgica, 

 but in some positions the same double contour of the tip of the prow is visible. 



The tube (Plate CXVIII, figs. 5 — 5 b) is gently curved and finely tapered, especially 

 in the smaller specimens, and composed of finer sand-grains than in Lagis Koreni, neatly 

 cemented together, the tubes of young forms especially having very minute grains, and 

 in any case the tubes are perfectly rounded and apparently smooth, for the slight 

 elevations caused by the sand-grains are only visible under a lens, and a certain amount 

 of translucency is present, for the quartzose sand-particles are each fixed in its setting 

 like a jewel, so that there is little interference with the light. Moreover, the tube has 

 only the thickness of such grains, with a delicate coat of the secretion internally. The 

 smaller end of the tube has grains considerably finer than the wider, but they blend into 

 each other so insensibly that it is only by comparing the distant parts that the difference 

 is observed. Like many others the annelid works at its tube only during the night. 

 In the " Porcupine" Expedition of 1869 empty tubes occurred in deep-sea mud in which 

 no sand-grains were present, the only convenient hard particles being fragments of the 

 siliceous spicules of sponges, the animal constructing its tubes of these with the utmost 

 neatness and regularity in horizontal rows from end to end, somewhat after the manner 

 of close basket-work (Plate CXVIII, fig. 5 a). The fragments are short, and conduce to 

 the perfect rotundity of the tube, which only presents the slight convexity of each spicule 

 at the edge, the outline being minutely crenate under the microscope. The cement 

 fixing the spicule is in small quantity, just sufficient to render the tube strong without 

 interfering with its transparency and smoothness. The workmanship of these tubes, 

 indeed, excites admiration, no less for the skill and perseverance of the architect than 



