242 THE ANNELIDA POLYCHAETA. 



neurocirrus, that is, the one of the third somite, is a short, stout, subconical 

 process; and the second and third are intermediate between the first and the 

 fourth ; the fourth and immediately succeeding ones are long, cylindrical processes 

 bearing apically a much smaller, irregularly conical lobe; this general form is 

 retained toward the caudal region, but the cirri become shorter and shorter 

 and are often constricted proximally; in the posterior region they again take on 

 the conical form without distinction of a distal lobe, finally becoming very small 

 and almost obliterated. 



The typical acicula, as occurring throughout except in the most anterior 

 region, are black, stout, straight, excepting for a slight curve distally, with the 

 acute tip projecting among the bases of the setae, as usual. Only one aciculum 

 occurs in each parapodium. The dorsal acicula are represented, in the anterior 

 region at least, by a small fascicle of fine pale fibers extending into the base of 

 the notocirrus. The first true aciculum that could be detected by surface 

 examination is in somite XXV, in which the first crochet also occurs. 



The setae are of the usual four types. The crochets occur first on or near 

 the twenty fifth somite. Each crochet is very dark, blackish, excepting the 

 colorless, nearly transparent tip. The shaft widens conspicuously distad half- 

 way to the tip and then narrows to the teeth. Each is weakly doubly curved 

 and bidentate, with the tips of the teeth directed caudad. The subapical tooth 

 is large, straight, and acute. The apical tooth is very much smaller, being 

 minute, nearly erect, and but slightly curved caudad. The transparent mem- 

 branous guards extend over the teeth, rising convexly between the two and 

 usually distinctly above the level of the apical one. (Plate 55, fig. 5). The 

 compound setae of each parapodium form a separate ventral fascicle, as usual. 

 They are coarse, with the shaft proximally cylindrical and of uniform diameter, 

 but at the upper end suddenly strongly clavately widened. The appendage 

 is distally bidentate. The apical tooth is long and rather slender, proximally 

 erect and distally strongly curved or hooked ; the subapical tooth is much smaller 

 and is straight, relatively thick at base. The edge of the membranous guard 

 is weakly convex between the subapical tooth and the subbasal angle; it does 

 not rise above the apical tooth. (Plate 55, fig. 6) . The setae of the dorsal fascicle 

 are strictly capillary; no limbi or wings are detectable; long, tapering, finely 

 tipped, the tip often curved, especially in the smaller ones. Among the capillary 

 setae are the pectinate setae. These have the usual general form. The cuneate 

 appendage is concave from side to side. At one end of the distal series of teeth 

 is normally a much longer, lash-like process, or flagellum. (Plate 55, fig. 7). 



