POLYCH^ETA BENHAM. 103 



dorsal surface is very convex, and the segmentation is obscured by numerous closely 

 set annulations. The ventral surface of the thorax is highly glandular, but no definite 

 " gland shields " are delimited, as the glandular modification of the integument extends 

 across the ventral surface from right to left unicinigerous nueropods; but on the last 

 three segments the outlines of the glands are evident. 



In the abdomen the ventral surface is deeply concave, crossed, however, by 

 segmental rounded, transverse ridges. 



The prostomium (figs. 124, 125) consists of two portions, viz (a) an anterior 

 freely projecting flap overhanging the mouth; and (6) a posterior thickened transverse 

 fold, which is almost entirely hidden by the basal portion of the second or branchi- 

 ferous segment. 



The prostomial flap, or upper lip, is slightly trilobed, the middle lobe being more 

 prominent than the later regions, from which it is marked off by a slight notch on each 

 side. The middle lobe is inclined forwards and upwards, and has a somewhat thickened 

 free edge. On raising the prostomial flap, or on looking into the mouth from in front 

 (fig. 127), the base of the prostomium is seen to be continuous, with a transverse lobu- 

 lated structure, or " supra-oral arch," which is separated from it by a furrow. The 

 right and left extremities of this arch touch the upper part of the lower lip on either 

 side ; the median portion of it is smooth, and traversed by a number of fine furrows 

 radiating from its base forwards towards its edge; the lateral portions are thick and 

 swollen. 



The buccal segment or per'stormum is represented dorsally by a rounded trans- 

 verse ridge, overlapped and concealed by the branchiferous segment. Ventrally 

 however, it is produced forwards to form a great lower lip, which is separated from the 

 lateral region of the prostomial flap by a deep, horizontal cleft on each side, and it is 

 evidently very mobile (fig. 126). 



Between the upper and lower lips there projects a folded membrane (fig. 127), 

 which occupies the entire oral cavity. At first I supposed this to be a part of the gut 

 everted, but found on dissection that it has the following relations, from which it is 

 clear that it represents the series of tentacles of other Ampharetids. The free edge of 

 this : ' tentacular membrane " is thickened in the median region, but becomes thinner 

 towards each side. It is folded much in the way that a partially closed fan is folded, 

 but the folds are few and irregular. It arises from the under surface and posterior 

 margin of the " supra-oral arch " above mentioned (fig. 123), which is thus seen to 

 correspond to the tentacle-bearing ridge of other genera. The line of origin of the 

 tentacles is at about the level of the junction of the arch with the prostomial flap. At 

 this point as was seen by slitting open the body wall the buccal cavity (or oesop- 

 hagus ?) commences ; this is a tube with a thick, muscular wall, whose inner surface is 

 thrown into a number of rugae. Its floor is produced forwards to form an internal lip , 

 such as that figured by Fauvel (1897) for AmpJiarete grubei. 



