1923] NATURAL SCIENCES OF PHILADELPHIA 181 



compressed, the seta fascicle larger, but less spreading, and the 

 post-setal lamella more foliaceous, broader, stouter, triangular, 

 and curved dorsad to a semi-erect position that diminishes caudad. 



On the fifth and succeeding somites, the two rami are much 

 more closely united, the notoiwdium directed laterad instead of 

 dorsad, the notopodial setigerous tubercle laterad, and the post- 

 setal lamella small and broadly triangular. The reduction in width 

 of the body from this point caudad is due chiefly to the diminution 

 in size of the parapodial bases, the notopodia at the same time 

 again assuming gradually a more dorsal and erect position, and 

 developing a filamentous tip to the post-setal lamella. This 

 condition reaches its maximum at XVII with the appearance of 

 the dorsal transverse fold, in which the noto]iodium becomes 

 completely involved a few segments further caudad; it then assumes 

 a more lateral position with the post-setal lobe diminishing in size 

 to a delicate filament which appears like an appendage to the 

 transverse membrane and so continues to the end of the piece 

 (somite XL). 



At VI, the neuropodium is thickened and the post-setal lobe is 

 short, thick, blunt, and fleshy, ending in a small round projection 

 bearing several small marginal nodules, pro])ably sense organs. 

 The fleshy thickening quickly becomes reduced and at IX is practic- 

 ally gone. At the same segment, the fascicle of capillary setae 

 becomes smaller and dorsal, and posterior to it ai)pears a conspic- 

 uous black spot which increases in size for five segments and then 

 abruptly disappears. At this point (XV) the neuropodial setie have 

 become reduced to a minute fascicle in a strictly ventral position 

 and a delicate interpodal membrane appears, uniting successive 

 parapodia at the level of the dorsal border of the neuropodia. This 

 soon becomes a continuous fold forming a series of lateral pockets 

 between the successive transverse folds. There is no trace of liran- 

 chial or ventral cirri on any segments. 



Setffi all simple, faintly colored, but the thicker parts dull and 

 opake from internal granules. Anterior notopodials form large, 

 spreading, fan-shaped fascicles of numerous slender capillary setie 

 which curve high over the back. Dorsalmost much the longer, 

 becoming progressively shorter ventrad. Passing caudad, they 

 become fewer, straighter, and somewhat shorter. 



Anterior neuropodials (beginning on III and reaching to IX or 

 X) form dense fascicles of very numerous setae similar to the noto- 

 podials but shorter and more strongly curved. They quickly 

 become shortened, forming a dense palisade of very short abruptly 

 tapered seta?. This palisade is then gradually reduced from the 

 dorsum, and the ends of the seta? become even more abrujitly 

 tapered and provided with a short filamentous tiix All through this 

 region one or two larger and stouter setae stand abruptly out as a 

 distinct fascicle from the ventral end of the neuropodium. Appar- 



