500 AEIOIA CUVIERI. 



thirty-one segments anteriorly it is the twentieth, about five free papillae, that is, beyond 

 the foot, occurring at the eighteenth foot. At the nineteenth, twentieth, twenty-first, 

 twenty-second, twenty-third, and twenty-fourth the papillae extend to the mid-ventral line 

 along the anterior edge of the segment. The ventral rows of bristles attain their maxi- 

 mum development about the fifteenth or sixteenth foot, where there are twenty-one, and 

 diminish subsequently, the last occurring on the twenty-first foot as a small patch 

 considerably less than the first. The dorsal cirrus increases in size in its backward 

 progress, and shows an enlargement at the base. 



The dorsal bristles (Plate LXXXV, figs. 7, 7', 7") are finely tapered and marked by 

 minute transverse rows of spikes, which give a camerated aspect to the structure. They 

 curve inward towards the branchiae anteriorly, but after the alteration of the feet they 

 project over them. The strong, brown, curved spines of the ventral rows (Plate LXXXV, 

 figs. 7 a and 7 6) do not, in those best developed, show any trace of the camerated con- 

 dition, but so many intermediate forms occur that it is not improbable that originally the 

 majority sprang from such at first. In glancing along the ventral divisions of the feet, 

 the strong brown spines of the posterior row become distinct about the sixth foot, and 

 increase in size in the following feet. The rows of papillae behind the spines and bristles 

 of the anterior feet evidently perform important functions in the operations of the region. 

 They all slope backward. 



The twenty-second foot (Plate LXXVI, hg. 5 a) inaugurates a change in the structure, 

 for, whilst the branchiae continue as before in the mid-dorsal line, the ventral division has 

 no rows of strong bristles. The dorsal division has in front a long tuft of camerated 

 bristles tapering to fine points, and behind the large dorsal cirrus. Below, after an 

 interval, is another smaller cirrus, then a setigerous process with a long papilla, and a 

 few very slender bristles of the same type as the others (camerated). Lastly, the papillae 

 form a row to the mid-ventral line. The function of these ventral papillae may be con- 

 nected either with tube or tunnel in sand. This type of foot (Plate LXXVI, fig. 5 b) is 

 continued to the thirtieth, and then the camerated bristles disappear, simple long tapering 

 bristles taking their places in both divisions of the foot. 



The posterior feet show to the exterior of the large flattened branchial process a long 

 tuft of bristles wi th a knife-shaped cirrus behind it, the cirrus having a narrow pedicle 

 with a broad blade tapering to a point beyond it (Plate LXXVI, fig. 5 c); then comes a 

 cirrus, followed by the ventral division in the form of a bifid process with a long tuft of 

 tapering bri sties, and a short conical ventral cirrus externally. The foot is dorsal in 

 position, even the ventral cirrus being dorso-lateral. 



The branchiae, as Claparede so clearly showed, 1 have two vessels, with a numerous 

 series of transverse or connecting trunks. 



Only twenty ventral rows occur in an example from S.W. Ireland (122), but the 

 papillae are larger. Another small example, dredged at 422 fathoms during the * Porcu- 

 pine ' Expedition of 1869, had only nineteen of the bristled rows of the ventral division. 

 Moreover, whilst the strong upper brown spines showed no trace of transverse markings 

 (camerae) the inferior did so. The great thickness of the upper spines made it probable 

 that either a new growth had taken place in the bristle sac, or that an increment had 



1 ' Recherches sur la Struct. Annel. Sedent./ pp. 106, 109, and 192-3, pi. xiv, figs. 3 and 4, etc. 



