1905.] NATURAL SCIENCES OF PHILADELPHIA. 567 



any indication whatever of a ventral involution. There are 15 pairs 

 of plume-like branchiae, each very long and graceful anfl without any 

 trace of an interbranchial membrane. The stems are more convex 

 externally than those of P. sylendida, but stDl distinctly flattened, and 

 there is no trace of eyes. The barbs are all very slender, 2-ranked, well 

 separated and increase regularly in size from very short ones at the 

 base to very long ones, much exceeding the diameter of the thorax 

 toward the end ; in the distal \ they again decrease, leaving a short tip 

 entirely free from them. 



The dorsal lobes of the collar are narrow and very long, considerably 

 exceeding the second segment in length, with nearly parallel sides and 

 rounded ends, the two separated by a ^^ide dorsal fissure. The dorso- 

 lateral notches are very deep but narrow and not occupied bj^ a small 

 lobe. Laterad of the notches the collar rises nearly to the height of the 

 dorsal lobes, which it somewhat overlaps by means of low, broad exten- 

 sions toward the median line. The remainder of the margin is even 

 and scarcely crenulate, the ventral lobes arising regularly and gradu- 

 ally, without the formation of any notch, into prominent triangular 

 lobes overlapping the bases of the branchiae and separated by a deep 

 median fissure. 



The single example is fortunately complete. It measures 122 mm. 

 long, the thorax being 15.5 mm. and the branchiae 32 mm. long, and the 

 former 3.5 mm. wide. It is consequently long and slender, tapering 

 to the pygidium in the posterior -^-. There are 14 (13 setigerous) tho- 

 racic somites and 162 abdominal somites. The former region is 

 scarcely depressed and the remainder of the body nearly cylindrical 

 from pressure of the tube. Besides being unusually broad and deep 

 anteriorly the dorsal fissure is prolonged into a faecal groove extending 

 for nearly the length of the thorax, but gradually fading out behind. 

 The thoracic segments are ^ as long as wide, the middle abdominal 

 about ^ as long as wide, and the posterior very much shorter. Ventral 

 plates are developed much as in P. splendida, but the thoracic are rela- 

 tively longer and the lateral notches divide them unequally, being 

 nearer to the posterior border; the anterior abdominal plates are twice 

 as wide as long and the posterior 4 times or more, all very thick and 

 deeply divided ; none of the al)dominals are notched laterally, and they 

 occupy about ^ of the body width. 



Thoracic setae tufts are short and straight, the anterior ones placed 

 at a very high level. The tori of III have a length of nearly ^ the cir- 

 cumference of the body and are separated by ^^entrally -J- this distance. 

 From the first they decrease in size regularly, the last and shortest 



