NAINEREIS MAMMILLA.TA. 519 



but others are cracked. It may be that enlargement of these occurs after fracture, 

 though some of similar form in a developing condition have been seen in the tissues. 

 The prominent ridge of the foot ends in a notch ventrally, and the surface trends to the 

 mid-ventral line. 



A change occurs at the fourteenth foot, and is well marked at the twenty-third 

 (Plate LXXXVII, fig. 5 a), the slightly tapered dorsal cirrus having in front of it a group 

 of long tapering bristles with smooth shafts and serrated tips (Plate LXXXVI, figs. 2 b 

 and 2//). These are supported by about four spines. Moreover bifid bristles appear 

 in the dorsal division about the twentieth foot, and continue to the posterior region. The 

 shafts in the twentieth foot are rather strong, cylindrical, and translucent, and further 

 show, by the play of light, indications of serrations, though none are actually present. 

 The limits of the fork are " finished " distally and slightly enlarged, and the inner edges 

 are spinous. A low rounded papilla closely adjoining the foregoing represents the 

 inferior division of the foot and has two spines which pierce the tip, and a few slender 

 serrated bristles. The edge below is boldly convex. 



The chief changes in connection with the posterior feet are (1) the diminution in the 

 convexity of the body-wall below the foot, (2) the diminution in the size of the dorsal 

 cirrus, (3) the increase in the size of the ventral division of the foot, and (4) the appear- 

 ance of a ventral cirrus beneath it (Plate LXXXVII, fig. 5 b) a little in front of the tail. 

 The bifid bristles of the dorsal division are continued posteriorly, and they have stout 

 shafts, the sides of which present serrations, the bifid tip being short but stout, the inner 

 edges being spinous, and the terminal spine on each side projecting beyond the truncated 

 ends of the bifid region. 



CErsted (1843) added little to the account of 0. Fabricius, but he gave recognizable 

 figures and grouped the form under the Ariciaa, a family of his Cha?topoda Terricolina. 



Grrube (1851) included Nainereis in his last family of the tribe Papacia of the 

 Appendiculate Polycheeta. 



A young form found in Lithothamnion between tide-marks, Shetland, July, 1871, 

 belongs to this species. The snout is bluntly rounded, and is followed by two double- 

 ringed segments. The bristled segments are forty-two or forty-three, and the caudal 

 cirri are comparatively large. It is about 6 mm. in length. 



The original account of 0. Fabricius (1780) is fairly complete, without touching on 

 the microscopic characters of the bristles, and shows how acutely this zoologist had 

 observed Nature. Even the habits and food of this species did not escape him. 



It is probable that the Scoloplos minor of CErsted 1 is this species. The author 

 describes the head as globose, and the tail is furnished with four filiform appendages. 



The head of Theel's Aricia Tullbergi, from Nova Zembla, agrees in outline with this 

 form, but in other respects it differs, notably in the absence of dorsal bristles, yet the 

 latter may have been accidental, for such is a very exceptional condition in the group. 



2. Nainereis mammtllata, Glaparede. 



Cunningham and Pamage found an example which they referred to the above species 



1 ' Kroyer's Nat. Tids./ 1842—3, p. 125. 



