268 PROCEEDINGS OF THE ACADEMY OF [April, 



equal to the length of the prostomium and a length of nearly one- 

 third the body, grooved and crenulated for the entire length, narrow 

 at the base and becoming gradually thicker toward the distal end. 

 One specimen bears a pair of minute branchiae on this segment; on 

 the other they begin on the following segments. The branchiae are 

 very delicate extensile vascular filaments, which in all cages arise in 

 actual contact with the dorsal side of the notopodium. In perfect 

 specimens they probably occur on every segment except about twenty 

 at the caudal end, but in both of the two here described they are small 

 or absent on many of the middle ones. In the anterior depressed 

 region they are more firmly attached and longer than elsewhere, 

 occur regularly on every segment and form a crowded tangled mass. 



Setae perfectly simple, colorless, smooth, slender capillaries, forming 

 small, spreading, fan-shaped notopodial and neuropodial tufts; except 

 that the notopodials are longer than the neuropodials and the anterior 

 longer than the posterior they are all exactly alike, the longest equaling 

 one-half the body diameter. 



Color of male pale brownish, of female deep slate color. 



Since the type of the genus Heterocirrus has been shown to be an 

 epitokous phase of Dodecaceria, the next available name for such 

 forms as Heterocirris multibranchis and the present species is Tharyx 

 Webster and Benedict. 



Dodecaceria paoifica (Fewkes) (Plate IX, fig. 44). 



Sabella Pacified Fewkes, Bull. Essex Inst., XXI (1889), pp. 132, 133; 

 PI. VII, figs. 1, 2. 



More than a score of well-preserved examples of this species permit 

 of the preparation of a description more complete than the original. 



Usual length 30 to 40 mm., but sometimes extended to nearly twice 

 that length; maximum diameter about 1 mm.; number of segments 

 from 90 to 110. 



Body generally terete, usually slightly enlarged in the middle and 

 tapered a little each way, but often depressed and distinctly widened 

 at the posterior end; irregular enlargements and constrictions often 

 present at one or two other points. When depressed the venter is 

 flat, the dorsum convex. 



Prostomium and peristomium completely coalesced, together form- 

 ing a subcorneal head about one and one-half times as long as wide, 

 entirely without definite appendages, but with a pair of small dorsal 

 spots which probably represent the nuchal organs. The anterior 

 half, representing the prostomium, is a somewhat scoop-like, broadly 

 rounded lip deeply excavated below and overhanging the mouth, 



