1911.] NATURAL SCIENCES OF PHILADELPHIA, 271 



neurocirrus begins to undergo rapid reduction, and by the eleventh 

 its conical form and cirrus character are lost and it has assumed the 

 form of a low, smooth, rounded, opake and whitish swelling, which 

 increases in size to about XXV and then diminishes gradually, though 

 it remains as a small whitish spot even at the end of the piece. The 

 postsetal lobe retains its character longer, undergoing very gradual 

 reduction after X and shifting more ventrad. Even at XX it is quite 

 as long as the body of the parapodium and of a short conical or sub- 

 triangular form. At L (fig. 60) it is a minute blunt papilla, ventro- 

 caudad of the seta tuft, and farther back disappears altogether. 

 Notocirri become more slender, but retain their length, continuing to 

 reach the middle line as far back at least as the eighty-ninth segment. 

 In the middle region the bodies of the parapodia are reduced and 

 somewhat compressed and bluntly rounded, and are situated near 

 the level of the dorsum. 



On the three specimens known the gills begin as single filaments 

 on somites VIII or IX and never possess more than four filaments, 

 and that number only rarely. Two filaments appear at from XXII 

 to XXVI, three at from XXXIII to XL and continue to LVI or LXIX 

 where the number is reduced to two again and so continues to the end 

 of the several pieces. Not infrequently a segment fails to develop 

 a gill on one or both sides and frequently the number of filaments is 

 below the normal of the region. The gills, though of few filaments, 

 are typically pinnate (fig. 60) and the filaments rather thick and short, 

 the longest very constantly reaching just to the median line. They 

 arise on the dorsal side of the notocirri on a common notopodial base. 



Acicula of anterior neuropodia usually three, yellow, stout, tapered, 

 gently curved and terminated by long freely projecting mucronate 

 tips. On posterior neuropodia there are often only two acicula which 

 are like the anterior ones except that they are rather abruptly bent 

 near the distal end. Notopodial acicula are thi-ee or four delicate 

 fibers which enter the base of the notocirrus. 



Setae are of vitreous structure and all more or less yellow, the more 

 slender ones being very pale, the stouter ones deeper. The usual foui- 

 kinds occur, but they present greater variation and more transition 

 forms than usual. Ai-ticulated crochets (PI. X\TI, figs. 61, 62) are 

 confined to the first eight parapodia. On the first three they occur 

 in an irregular, open, vertical, preacicular series of three or four, one 

 or two on the acicular tubercle beneath the aciculum and one post- 

 acicular — about six or seven in all. On the fourth foot (V) those in the 

 dorsalmost part of the fascicle are replaced by simple acute seta?, Ijut 



