1904.] NATURAL SCIENCES OF PHILADELPHIA. 489 



have the following average distribution and complexity : Begin on 

 V with one filament, 3 on VI, 5 or 6 on VII, 6 to 8 from VIII to XXX, 

 4 or 5 to XXIX, 3 to XLII, 2 to XL VI, 1 to LIV, and cease by LV. 



The first parapodium (III) is supported by a pair of pale yellow, 

 simple pointed, sharply bevelled aciculi (PI. XXXVII, fig. 13), and 

 bears a small number of ventral compoimd and dorsal capillary setse, 

 as well as one or two spatulate setse. On IV the number of each kind, 

 especially the last, is increased. By VI the typical number, size and 

 arrangement is attained. The neuropodial aciculi are two or rarely 

 three, stout and blunt, and in the case of one somewhat enlarged at the 

 end (PI. XXXVII, fig. 14). Between XL and L a single ventral crochet 

 appears, and the dorsal aciculi become tapered and slightly curved 

 at the end (PI. XXXVII, fig. 15). The number of both compound 

 and capillary setse decreases in this region, and in the posterior somites 

 the latter seem to be absent altogether. The compound setse also un- 

 dergo a slight alteration in form. The dorsal cirrus throughout is sup- 

 ported by about three slender aciculi. 



The compound setse (PI. XXXVII, fig. 10) are all rather slender, 

 nearly colorless, have curved, finely striated stems moderately enlarged 

 at the ends ; the appendix is not over two and one-half times the great- 

 est diameter of the stem, the end is prominently hooked and bidentate, 

 the accessory tooth distinctly triangular, guard narrow, scarcely 

 covering the end. From the posterior branchial region caudad the 

 hook gradually diminishes, while the accessory tooth increases in 

 size, the base of the appendix becomes more oblique, and the end of 

 the shaft more strongly curved and thicker (PI. XXXVII, fig. 11). 

 Throughout most of the branchial region the compound setse are ar- 

 ranged in a nearly complete circle somewhat open both dorsally and 

 ventrally. 



The capillary setse form a dense dorsal tuft reaching far beyond the 

 compound setse. They are pale greenish or nearly colorless, curved, 

 finely pointed and faintly obliquely striated (PI. XXXVII, fig. 12). 

 Back as far as the end of the branchial region they exhibit a slight 

 enlargement in the outer third, but posteriorly are strictly capillary. 

 Spatulate setse (PI. XXXVIII, fig. 42) form a close dorsal tuft at the 

 base of the capillary. They are colorless and very delicate, the ends 

 half round with the outer angles prolonged and the distal margin 

 folded and split mto nine or ten processes tipped with short filaments 

 which bend abruptly inward nearly at a right angle. These setae 

 appear as a single one or two in the first parapodium and continue to 

 C at least. 



