ONUPHIS LITABRANCHIA. 277 



The postsetal process is markedly shorter on the second and third pairs, and soon 

 is a mere point and then essentially absent on the ninth parapodia. The neuro- 

 cirrus similarly becomes quickly reduced to a mere nodule and then obliterated. 

 The notocirri continue throughout the length of the body, but in the middle and 

 especially the posterior region have become shorter and much more slender. 



Branchiae first appear on somite VIII, the first appearance on this somite 

 being uniform so far as observed. The branchiae in the type are throughout 

 undivided, excepting the one case noted below, each consisting of a single fila- 

 ment arising on the dorsal side of the base of the notocirrus. Each of the first 

 branchiae is a slender filament of uniform diameter, more slender than the noto- 

 cirrus but much exceeding the latter in length; it does not reach the middorsal 

 Une. (Plate 51, fig. 8). Caudad the filaments increase in length, attaining the 

 middorsal line at or near somite XIII-XV and then a little farther caudad 

 surpassing it, the branchiae of each pair overlapping across the dorsum. (Plate 

 51, fig. 9, 10). Then the filaments again decrease in size and fall short of reach- 

 ing the middorsal line in the middle and posterior region. The right branchia 

 of the twenty first somite, unlike any other in the type, divides a little above 

 the base into two branches and one of these, which is somewhat the stouter, 

 again bifurcates toward the tip. In a paratype, however, beginning at somite 

 XXXII, and continuing on about the succeeding fifteen somites, the branchiae 

 are regularly bifilamentous, the bifurcation occurring a little above the base; 

 in many of these one filament again bifurcates higher up, or it may have three 

 branches. Caudad of this region the branchiae continue of the unifilamentous 

 form as in the type. (Plate 52, fig. 1). 



The neuropodial acicula seem to be mostly from three to five in number. 

 They are of the same color as the setae, but are much stouter. They first nar- 

 row gradually distad and then more abruptly, the free tips being very slender, 

 long, and acute and commonly more or less curved; they emerge among the 

 bases of the dorsal setae. The notopodial acicula, when detectable, appear as 

 slender, inconspicuous fibers entering the base of the notocirrus. (Plate 51, 

 fig. 2). 



The principal setae of the dorsal fascicles are long, slender, and of uniform 

 diameter until toward the distal end, where they narrow to a very slender, fine, 

 and acute tip, the narrowing portion of the setae being ordinarily curved, the 

 fine tip more strongly so; each of these setae is distinctly bilimbate, each wing 

 rather narrow, beginning a little proximad of the narrowing region of seta and 

 continuing distad to fade out on base of the fine tip. (Plate 51, fig. 3). Among 



