1923] NATURAL SCIENCES OF PHILADELPHIA 195 



tufts but no gills. Remaining thoracic segments are very similar, 

 well different iatcd l)y distinct furrows. Dorsally they are smooth 

 and arched, all, except the most anterior, with a transverse furrow 

 separating a shorter ])osterior, from a longer anterior annulus. 

 Ventrally slightly flattened, with rather conspicuous ventral plates 

 which })ecome more i)r()minent to XIX where they abruptly 

 cease, there being none on the last thoracic segment. 



Parapodia well developed, with prominent setigerous tubercles 

 from IV to XX, bearing flat tufts of setse. Uncinigerous tori begin 

 on V. The second is the longest, equaling about | of the circum- 

 ference of its segment. Succeeding segments decrease regularly 

 in length to the last which is slightly more than h as long as the 

 second; first about equals the eighth or ninth. Small cirri, retractile 

 into pits, occur just above and behind the seta^ tufts of \l and 

 VII, but are much smaller than those of P. brevibranchiata. 



Gills two pairs, arising from tubercles on the extreme dorso- 

 lateral region of II and III, easily detached and regenerated and 

 consequently always of unequal size, the left anterior being largest 

 on the type and one other, the right anterior on others and the left 

 posterior on still another; several have all gills missing. When 

 fully developed they are very large and bushy, and conceal the 

 anterior end of the body. Stalk short, thick and flattened, divided 

 abruptly into several (about 5) large i)ranches, which immediately 

 subdivide repeatedly six or seven times to the terminal filaments. 

 The branches are long, low, spreading, and densely crowded, 

 prol^ably giving in life an aspect very different from the smaller 

 and more erect gills of P. brevibranchiata. The smallest and pre- 

 sumably youngest gills are simpler, with the main ])ranches only 

 developed, others appearing with increase in size. 



Colorless in preservation except the doi'sum of the first five 

 segments which are deep brown and very highh' vascular. 



Setie form conspicuous tufts and exce])t that they are stouter 

 and have less prolonged tips are similar in form and arrajigement 

 to those of P. brevibranchiata. Unicini (Plate XVII, fig. 9) of tiioracic 

 segments with prominent stout beak and high full crown, c()nii)osed 

 of about six transverse series of numerous crowded teeth. Guard 

 well developed and breast full and prominent. On anterior somites 

 they have the prolonged stem-like bases characteristic of the genus, 

 but behind X, where the setse are arranged alternately in two 

 rows facing each other, they are more slender, with fewer teeth in 

 the crown, more delicate guards and the stout stem r(>])laced by 

 a delicate ligament. Abdominal uncini are much like the posterior 

 thoracic, but more delicate and possess long filamentous ligaments. 



Several are enclosed in fragments of thick -walled tubes of fine 

 mud. 



Stations 4307, off Point Loma, 169-490 fathoms, green mud and 

 fine sand; 4331, same locality, 57-58 fathoms, green sand and rocks; 



