1911.] NATURAL SCIENCES OF PHILADELPHIA. 275 



shorter and bluntly rounded at the apex ; at the sixth it is replaced by 

 an oval glandular swelling, which increases in area but becomes less 

 elevated for six or seven segments and then undergoes gradual reduction 

 in the post-branchial region. After the appearance of the gills on VI 

 the notocirrus also undergoes reduction, but so gradually that a small 

 cirrus is still present on the one hundred and twenty-first segment. 

 The postsetal lobe becomes smaller simultaneously with the notocirrus, 

 but much more rapidly, soon becoming minute and shifting to a post- 

 setal position and practically disappearing by the end of the branchial 

 region. 



Gills begin on somite VI and continue to XLIX to LI I on the 

 several specimens. They arise on the dorsal side of the base of the 

 parapodia by a stout base, on the ventral or lateral side of which the 

 neurocirrus is borne (PL XVIII, fig. 78). Several anterior pairs are 

 very large, the second in all cases exceeding all of the others and 

 reaching quite to the tip of the notocirrus of the opposite side, the 

 first being about seven-eighths and the third about three-fourths or 

 more as long as the second. Succeeding ones diminish in length, at 

 first rapidly, then slowly, the eighth equalling the body width, the 

 twenty-first reaching the middle line, the forty-first being only as 

 long as the notocirrus. Anterior gills are tall and slender when fully 

 extended, being shaped much like Lombardy poplar trees. The 

 trunks have stout, feebly annulated bases above which they taper and 

 are spirally twisted, bearing numerous, rather short spirally arranged 

 filaments which become smaller distally. This spiral arrangement 

 of the gills persists to at least XXXV, the number of turns varying 

 with the length of the gill, the second and longest having twelve. 

 Beyond somite XXXV, the trunks have become so short and the 

 filaments so crowded that the appearance is brush-like. At XL there 

 are only three short filaments, and the last seven gills consist of a 

 single filament, each of which gradually diminishes in length. 



Neuropodial acicula three or four, tapered, curved, terminating in 

 acute tips projecting beyond the end of the acicular process. Noto- 

 podials one or two delicate rods or a bundle of fibers. 



Setee of the first four parapodia (II-V) chiefly compound crochets 

 (PI. XVIII, 79 and 80) arranged in a loose vertical preacicular series 

 of about six or eight, of which one, much stouter than the others, is 

 subacicular and one more slender postacicular. The latter (fig. 80) 

 has the appendage considerably longer than the rest. All have the 

 articulation well-developed, the end very strongly hooked and provided 

 with a prominent accessory spur and well-developed guard, the end of 



