PROCEEDIiSrGS OF THE NATIONAL MUSEUM 



VOL. 79 



The holotype has the basal portion of the prostomium (fig. 3, a) 

 rounded and carries two pairs of reddish eyes, those of the anterior 

 pair much farther apart than are the posterior. Just in front of 

 the anterior eyes the prostomium narrows, and for a distance of a 

 little more than twice its width it is continued forward as a parallel- 

 sided lobe with rounded apex. The first somite is narrow on the 

 dorsal surface (the boundary between this and the prostomium is 

 not clearly marked off in my material), but laterally and ventrally 

 it is continued forward in the form of an inverted hood underlying 

 the prostomium for nearly its entire length and folding laterally so 

 as almost entirely to obliterate it in a side view. When extended, 



the proboscis is 2-lobed 

 at the apex extending 

 only for a short dis- 

 tance beyond the end of 

 the prostomium ( fig. 3, c ) . 

 I was unable to find 

 any trace of tentacular 

 cirri on any of this 

 material. 



The first setigerous 

 somites have each a 

 flattened cirruslike lobe 

 posterior to the dorsal 

 tuft of setae. From the 

 first to the third there 

 is gradual increase in 

 size of these lobes and 

 then a gradual decrease, so that they practically disappear in the 

 region of setigerous lobes 8 to 10. Similar but smaller lobes lie 

 posterior to each seta tuft in the neuropodium. (Fig. 3, b.) 



In this material the structure of the gills varies much in different 

 specimens. So far as I can determine, the number should be three, 

 but fewer are present in some cases, apparently because of loss. A 

 fully developed gill has a naked base and a heavy central axis, car- 

 rying on either side a row of filaments, the longest filaments being 

 in the middle of the series. The gills shown in Figure 3, b, repre- 

 sent three stages in gill development. First there is a slender ten- 

 taclelike process with crenulated margins from which later filaments 

 grow out, as in the second of the gills figured, and finally these 

 develop into the conditions shown in the third gill. The most pro- 

 fusely branched gill I have seen was the first pair in a specimen that 

 retained no others. Apparently, therefore, the first gill does not 

 always retain the teniaclelike character shown in the figure. 



Figure 3. — Prionospio plmnosa, new species : a. Dorsal 

 view of prostomium, X 45 ; 6, side view of pros- 

 tomium, X 20; c, protruded pharynx, X 20 ; d, seta, 

 X 500 



