150 [Assembly 



Brancliire behind and a little within the tentacles ; reach back to 

 the seventh or eight segment ; widest in the middle, tapering uni- 

 formly in both directions, except tliat near the top they are suddenly 

 constricted, ending in a short cylindrical process ; they are flattened 

 below, carinate above, giving a triangular cross section for most of 

 their length ; edges thin, and thrown into deep, rounded folds or 

 scollops. Both tentacles and branchiae are densely covered with 

 long cilia ; turned forward they completely cover the head ; the 

 setae of the first segment, both dorsal and ventral, are similar to 

 those of the next five, but are a little shorter. 



Second segment, covered dorsally by a raised membrane, forming 

 a pouch ; the free anterior margin of this pouch is deeply concave ; 

 its elevation above the dorsum equal to the thickness of the body ; 

 at the sides it passes into the dorsal cirri (lobes). 



Dorsal cirri : back of each fascicle of dorsal setffi, on the first ten 

 segments, is a broad, rounded plate or lobe ; back of the tenth seg- 

 ment this plate gradually becomes narrower, until it is changed into 

 a short, conical cirrus, which remains to the end. 



Yentral cirri : on the first six seajments behind each buneli of 

 ventral setae is a lobe similar to the dorsal lobe, but smaller ; at the 

 seventh segment it disappears. 



Dorsal setae, capillary ; those on the anterior segments (fig. 48) 

 wider and shorter than those further back (fig. 49) ; ten to fifteen 

 in each fascicle in front, gradually decreasing in number till only 

 four or five are found on the posterior segments ; they are arranged 

 along the lateral line of the dorsum, and point upward ; the ventral 

 setae of the first six segments are similar to the dorsal, but less nu- 

 merous, and a little shorter; back of the sixth segment the capillary 

 setae are nearly replaced by uncinate setae — a few, however, remain- 

 ing in the lower part of each series, even to the end ; the uncini 

 (fig. 50) are arranged in a single, transverse series, three to five 

 in number, quite short, hardly projecting beyond the surface ; they 

 become gradually more numerous, each series having from eight to 

 twelve on the posterior segments, at the same time growing a little 

 longer ; they have four terminal teeth, the outer one being shortest 

 (fig. 50), and are covered by a delicate membrane. 



Anal segment with slightly thickened, rounded margin ; no appen- 

 dages. 



Body slightly convex above, flattened below. 



Color : tentacles colorless ; branchiae dark green, with transverse 

 bands of light green or yellowish-green ; body colorless or light 

 flesh-color ; a few specimens with the first eight segments dark green. 



Length of adult, 6™™ ; width, 0.6""™ ; number of segments, 70. 



Found in great numbers on beds of Mytilis edulis / also in ditches 

 to which the tide water had access, very near high-water mark ; the 

 only other annelid found under the same circumstances being Nereis 

 limhata Ehlers ; the first specimen taken was on a shell, dredged. 

 This species lives in dirt tubes, which they leave very readily when 

 disturbed, and move about rapidly with quick, jerking motions of 



