DODECACERIA CONCHARUM. 257 



In some the colour of the body is brownish-red anteriorly, greenish-yellow posteriorly, 

 and streaked longitudinally with the red blood-vessel. In others touches of orange are 

 present. The annelids dye spirit green and the body assumes a blackish-brown hue, paler 

 posteriorly, the tip of the tail, however, becoming blackish-brown. 



The first seven bristled segments have on each side two fascicles of simple bristles 

 (Plate 0, fig. 1) which taper to very delicate tips. In the eighth the ventral division 

 shows a few of the peculiar bill-hook forms amongst the bristles, and at the tenth the 

 crotchets only occur in the ventral division. 



In some at the tenth foot the dorsal division has a few of the simple tapering 

 bristles, and about three stouter bristles, the tips of which have been abraded so that an 

 oblique surface remains at the end of the stump. 



The typical hook (Plate CVII, fig. 7 b) has a slightly curved shaft which somewhat 

 increases in diameter from the base to the distal third, then gently bends backward to the 

 neck, where the dorsal line again has a backward curve, then forward to the tip. The 

 anterior curve (which at the neck is also slightly backward) (Plate CVII, figs. 7 and 7 a) 

 is abruptly broken by a bold conical projection, from the apex of which the distal curve 

 runs to the stout tip. It thus differs in all respects from the tip of the southern Dodeca- 

 ceria ater, De Quatrefages. 



In the posterior part of the body the dorsal setigerous cone bears a few of 

 the long slender tapering bristles and one or two short stout hook-like bristles 

 bevelled at the tip, and representing a modified type of the ventral series. These modified 

 hooks have no enlargement on the anterior face below the bevelled region. The ventral 

 division likewise has a bristle or two of a shorter type than the dorsal, which are con- 

 spicuous in a lateral view from above, and one or two of the bill-hook crotchets, the only 

 peculiarities being their shortness and the more marked curve of the less robust hook at 

 the tip. The conical projection at the anterior base of the curve is distinct (Plate CVII, 

 fig. Id). 



In boring in sandstone, as at St. Andrews, the key-hole tube is lined by a calcareous 

 secretion. Its habits are those of a true Cirratulid. 



In a young example, 3 to 4 mm. in length, procured along with young Arenicola, the 

 little boring Sipunculus, Pholoe and swarms of Polydora ciliata at the East Rocks St. 

 Andrews, the body (in spirit) is rounded in front, but the posterior third is more or less 

 flattened as in Heterocirrus ater. The colour of the two regions also differs, that in front 

 being pale greyish, whilst the posterior is brownish-red. The bristled segments are about 

 thirty-five in number. The snout is formed, as in the adult, with the mouth considerably 

 behind the tip, and the tentacles and the branchiae are well developed. The two rounded 

 papillae at the vent are more distinct than in the adult. The characteristic hooks show 

 that whilst the flattened posterior region simulates that of Heterocirrus ater, yet this is an 

 early condition. 



(Ersted (1844) mentions that he found in an example two pairs of tentacles in the 

 first segment placed one over the other, the lower much shorter and thicker than 

 the upper. He notes that the species abounds in oyster-shells along with Gliona, and that 

 perhaps the alimentary chyme (which contains muriatic acid) and the ventral hooks aid in 

 the perforations. 



156 



