314 PROCEEDINGS OF THE ACADEMY OF [April, 



leaving nearly smooth, solid capillary tips. On the posterior region 

 the more slender and elongated setse have the structure of the more 

 delicate parts of the anterior setse, the basal region with its canal being 

 absent and the shaft provided with minute appressed teeth. No 

 bifurcate setse, such as are present in A. johnsoni, can be detected in 

 this species. In the neuropodium it is evident after a few somites 

 that the shorter setse of the first rank or two have become dark-colored 

 and have lost both the external serrulation and internal cavity. These 

 changes become emphasized for several segments. Setse of the pos- 

 terior rows are of the same type as the notopodial setse, but have the 

 basal canalization and cameration more evident and the slender 

 solid tips less prolonged. At the ventral end of the fascicle is a small, 

 somewhat isolated tuft of shorter setse, some of which are simple 

 spines finely serrulated along one margin and a few short blunt spines 

 with the ends enclosed in a mucronate hood. All of these differentia- 

 tions become more pronounced to somite XI, after w^hich the stout 

 acicular spines appear in association with a conspicuous reduction in 

 the number and size of the other setse, particularly those of the anterior 

 rows. In this region the small ventral tuft is composed entirely of a 

 few small hooded spines (fig. 176), below which is a second tuft of the 

 largest canaliculated setse remaining on the neuropodium. In the 

 posterior region the neuropodial setse have exactly the structure of 

 the notopodial, but are fewer in number. 



Branchiae begin on somite V of all specimens, rising from the dorsal 

 area as a pair of foliaceous, rather broadly lanceolate processes barely 

 reaching to the notopodia and separated by a distance greater than 

 their length. Proceeding caudad, they regularly increase in length and 

 size (PI. XXI, fig. 172) until by somite XL their length is about 

 three-fifths the width of the body, their form foliaceous lanceolate 

 and posture erect. On the posterior piece they have become fully 

 one-and-one-half times the body width and taper to filamentous tips, 

 being therefore much elongated and very conspicuous (PI. XXI, fig. 

 173). They show no special areas of strong ciliation, but are very 

 richly vascular, having a large axial vessel with a spacious bulbous 

 expansion at the base and a complex bipinniform system of very nu- 

 merous lateral branches extending to the margins. Anteriorly the gills 

 are quite free from each other and from the notopodia, but as the 

 parapodia assume the dorsal position they become united by a trans- 

 verse membraneous fold that crosses the whole width of the dorsum. 



Proboscis very imperfectly known, only the ends of a few of the 

 lacinated divisions being exposed on any of the specimens. 



