PLATYNEREIS POLYSCALMA. 223 



wholly in the most caudal region ; the shafts of the compound setae become much 

 shorter and in the ultimate pairs only the simple notopodial ridged setae remain ; 

 the neuropodium becomes much reduced in the penultimate pair, having only 

 a small transparent aciculum and in the ultimate pair is scarcely at all traceable. 

 The last pair of parapodia are especially modified, being a little longer than the 

 penultimate paif and having the notocirri much thicker and longer, these pro- 

 jecting and looking somewhat like special anal cii-ri, while the neuropodium is a 

 scarcely obvious rudiment at the base on the ventral side. (Plate 31, fig. 7, 8). 

 The acicula are two in number excepting in the most anterior parapodia, 

 where there is but a single aciculum in each. The acicula of the anterior region 

 are dark amber colored, those of the posterior region pale yellow or proximally 

 colorless. Notopodial and nem'opodial acicula nearly equal in size and identi- 

 cal in form, acutely pointed and straight or, in the posterior region, distally a 

 little curved. The setae are mostly compound, a few in the last pair of para- 

 podia, however, being simple. Those of the nereid division are of both homo- 

 gomph and heterogomph types. The notopodials are homogomphs with but 

 slightly curved shafts marked by a single, narrow, transversely striate band. 

 The distal piece is long, slenderly acim^iinate, the naked tip being very fine and 

 usually curved; below this on one side is the usual dense series of short setae. 

 The neuropodials are of three types: — homogomphs hke the notopodials; 

 heterogomphs in wliich the distal piece is much shorter with the short naked tip 

 narrowly rounded and the series of setose teeth short, with the shaft at the 

 distal end presenting a second cross-striate band lacking in the homogomphs; 

 and heterogomphs in which the distal piece is hke that of the orcUnary homo- 

 gomph above described. The natatory setae of the parapodia of the posterior 

 division are homogomphs with shafts, as usual, strongly cross-striate and with 

 the longitudinal striate band double. The blades are of the usual general form, 

 being clavately widened distad, narrowed at each end. In the blade of the noto- 

 podials there is a weak incurving on one side below the apex; in these the mar- 

 ginal teeth toward the distal end along the incurved region are very long and 

 spine-hke and project at right angles to the surface, while proximally these are 

 replaced by the usual very short, fine teeth, the latter sometimes extending dis- 

 tad so as to overlap the longer spines. In the neuropodials the blade is some- 

 what longer, more abruptly narrowed distad, and the armed margin throughout 

 bears only the fine short teeth. In addition, the most dorsal notopodials repre- 

 sent a third type in which the blades are strongly transversely ridged or ribbed, 

 the ribs in the most dorsal extending nearly to the bases of the blades, while 



