326 



PROCEEDINGS OF THE ACADEMY OF 



[June, 



segments, represent a species much larger than P. magnifica, from 

 which it is distinguished by numerous characters. The type, consist- 

 ing of 40 segments, is 16 mm. long, 4 mm. in width of body and 7 mm. 

 between the tips of the setse. The prostomium is nearly quadrate 

 but slightly wider anteriorly, where the angles are rounded ; it is quite 

 deeply cut into two lobes by a median cleft posteriorly. The palpi are 

 broad, flattened, broadly rounded at the ends and slightly exceed the 

 prostomium in length ; at the base they are coalesced but diverge widely 

 and curve ventrad distally. The eyes of both pairs are reddish brown, 

 small and round, the anterior very little larger than the posterior and 

 directly in front of them or but little farther apart. The dorsal 

 cephalic appendages are imperfect on all of the specimens, but are 

 evidently slender, tapering, smooth and flagelliform. The middle 

 tentacle is apparently about S\ times and the lateral tentacles about 

 twice the length of the prostomium and palpi. The former arises 



PlonosylUs gigantea — a, parapodium XXV, without setse, X 24; b, parapoclium L, 

 without setae, X 24; c, a seta Avith blade of average length, from XXV, X 360. 



from the center of the prostomium, the latter from the anterior lateral 

 margins. The very short, slightly flaring proboscis bears 9 or 10 

 marginal papillse and apparently is unprovided with a strongly cuticular 

 region. 



The peristomium is extremely short above, where it is represented 

 chiefly by a fold of integument which conceals the posterior lobes of 

 the prostomium. At the sides it is better developed and ventrally is 

 crowded forward with the next two segments beneath the prostomium. 

 Its tentacular cirri are similar to the prostomial appendages, the dorsal 



