P0LYC1LETA. 299 



The description was based upon a single indifferently preserved specimen. If 

 confirmed it will probably form the type of a new genus or sub-genus intermediate 

 between Polymnia and Nicolea. 



The labium and lateral lobes of the third segment are of the same nature as the 

 corresponding processes in Loimia (Plate VI., fig. 143). 



Polymnia socialis, n. sp. Plate VI., figs. 146 to 148. 



Locality : Narrow sand- encrusted tubes of a small Terebellid were adhering to 

 the tubarium of PhyllochoBtopterus ramosus, trawled off Galle at Station XXXIX., 

 16 to 30 fathoms. One of the larger tubes measured about 50 millims. in length, 

 2 millims. in diameter. Three pairs of arborescent gills, the first (longest) extending 

 forwards beyond the upper lip. Seventeen pairs of capillary fascicles, sixteen pairs of 

 thoracic tori, uncini uniserial in the first six tori, biserial and opposite in the rest, 

 uniserial again in the abdominal pinnules, which are supported by fine sustentacular 

 setae. Capillary setae simple, narrowly limbate. The band of scuta ventralia is well 

 set off from the surrounding parts, rounded in front, attenuate behind, ending as a 

 whitish streak in the region of the 13th-14th tori, but continued behind this point as 

 a colourless median streak into the anterior abdominal region ; behind the 9th torus 

 the band of scuta becomes paler, whitish. 



The dorsal surface of the worm is smooth and convex, not showing segmental 

 divisions in the region of the thorax. The first segment which forms the lower lip is 

 long below and deeply cleft, the right half slightly overlapping the left (Plate VI., 

 fig. 146). The lateral lobe of the second segment, seen in side view, appears as a 

 sub-elliptical or semilunar, symmetrical free dermal fold. The uncini are remarkable 

 for the number of denticulations on the vertex, which exceed the narrow limits 

 suggested by von Marenzeller for the genus. The vertex of the uncinus, when 

 seen from above, shows a rosette of twelve denticulations, and attentive examination 

 shows that these are arranged in arcs across the vertex. The general formula for an 

 uncinus of this species, according to Marenzeller's system of notation ('Adriat. 

 Ann.,' hi., 1884, p. 163, or p. 13 of reprint) would be as follows : 1, 22, 333, 4444, 

 55555. The rosette which appears in vertical view is formed by the teeth of third, 

 fourth and fifth orders (Plate VI., figs. 147 and 148). 



The limbus of the capillary setae is, at least in some of them, wider over a sub- 

 terminal tract than more distally, spreading like a pair of narrow fins on either side 

 of the seta. The terminal portion presents a very narrow obscurely striated border. 

 This is merely the continuation of the limbus, and is not like the laciniate plumose 

 structure of the terminal filament in Amphitrite. In some setae from one of the 

 specimens the terminal portion is marked off by a shallow constriction from the 

 bulk of the shaft. This is not a constant feature however, and the setae of the 

 larger individual end normally in a simple point. 



Length of fore-body without the tentacular cirri (which are present knotted 



2 q 2 



