466 PROCEEDINGS OF THE ACADEMY OF [June, 



shrinks from the ventral margin, from which a few of its }:)apillse become 

 detached and appear quite isolated on the body walls of the posterior 

 somites of this region and the following transitional region; but such 

 papillae are few and small, and appear only on the lateral portions of 

 somites XVI to XXI or some of these; the dorsal margin of the 

 notopodial postsetal lobe, with its papillae, elongates until it appears 

 as a main stem bearing the remaining papillae on its lateral side. 



The 17th and ISth ]:)arapodia are transiticjnal but resemble those of 

 the posterior region more closely; they are, however, less dorsal 

 and usually exhibit a few papillae just ventrad of the parapodia. 

 The 19th is cjuite typical of the posterior region, directed dorsad from 

 the upper part of the sides of the somite, neuropodium narrow but 

 prominent and erect, with a small leaf-like ovate presetal process 

 having a strong basal constriction, a small conical recurved postsetal 

 process, and, below the constriction, a minute conical neuropodial 

 cirrus, apparently derived from the dorsalmost postsetal papilla; noto- 

 podium broader and much more conspicuous, consisting of a setigerous 

 tubercle and a greatly enlarged, pointed, ovate-lanceolate, postsetal 

 process nearly equalling the gill in length, with a constricted somewhat 

 flattened base, and an asymmetrical wing to the })lade-like extension of 

 its lateral margin. Changes in the parapodia toward the posterior 

 end consist in slight alterations in proportion of parts ; the entire foot 

 becomes more elongated and narrow^ the notopodial postsetal lobe 

 even larger and more leaf-like, assuming the form of the branchiae, 

 except that its base is always constricted, and the neuropodium more 

 reduced in size. 



Branchiae of nearly full size begin abruptly on the 5th setigerous 

 somite and continue as far as the material I'eaches toward the posterior 

 end; strictly dorsal, separated by ^ the width of the back; anteriorly 

 broadly, then narrowly Ungulate, pointed, broadly attached, with a 

 central axis containing 2 blood vessels connected by numerous trans- 

 verse loops arranged in doubly pinnate fashion; branchiae of a pair 

 united with each other and with the corresponding notopodia by deli- 

 cate transverse integumental folds. 



Setae all nrore or less tapering and acutely pointed. Neuropodials 

 arranged in a dense phalanx, very numerous, rather stout, of two kinds, 

 with transitional forms; those of the anterior ranks shorter, densely 

 fibrillated, olive colored, strongly curved in a more or less sinuous 

 manner, the edge corresponding to the i)rinciiml convexity distinctly 

 serrated with delicate transverse ridges partly encircling the shaft; 

 those of the posterior ranks much longer, more slender, less strongly 



