480 THE ANNELIDA POLYCHAETA. 



The branchiae on each side form a compact brush in which the closely 

 applied radioles are united proximally by a membrane. The branchiae in each 

 group number about thirty. Each branchia has a short, naked tip almost as 

 long as a pinna. (Plate 78, fig. 9). 



The operculum is a disc which is hemispherically elevated above. The 

 rounded elevation, which covers the entire upper surface, bears three spines, 

 of which the two posterior are longest, are proximally thick and distally pointed, 

 and are curved or reflexed outward and forward. The unpaired spine is short 

 and uncurved, broad at base and rapidlv narrowed to an acute point, being 

 roughly in the form of a very low, broad cone. Along each side of the stalk 

 and curving forwards beneath the disc is a conspicuous wing; the wings begin 

 beloM' the middle of the stalk. (Plate 78, fig. 8). 



The collar is ventrally high or long. In the midventral line it is notched, 

 the notch rather shallow and rounded at the bottom. Also notched on each 

 side. The dorsocephalic corner prominent, subrectangular, but with the apex 

 narrowly rounded. Caudad on each side the collar is evenly continuous with 

 the thoracic membrane, which is somewhat angularly elevated near the middle 

 of its length and extends to the caudal end of the thorax, where it continues 

 ventrally to unite beneath with the membrane of the opposite side. 



The dorsal thoracic setae are rather short and comparatively numerous in 

 each fascia. They are curved as usual toward the distal end and bear on the 

 convex side of the curved portion a conspicuous wing. (Plate 78, fig. 6). The 

 abdominal setae are all broken off. The uncini are very numerous in each series 

 on the thorax. Each uncinus bears at its cephalic end the usual distally blunt, 

 ventrally furrowed process, and caudad of this, excepting in the reduced ones 

 at ends of series, fifteen or sixteen fine, slenderly pointed teeth. (Plate 78, fig. 6). 



Locality. Paumotu Islands: Fakarava. 12 October, 1899. One speci- 

 men. 



From P. strigiceps Morch, known from the region of Australia and New 

 Zealand, this species is readily distinguishable by the marked differences in 

 proportion and structure of the operculum, e.g., the three spines or cornicles; 

 P. tricuspis Phil., common in the Mediterranean, has fewer branchiae and the 

 elevation on the operculum is higher, with the cornicles of very different form. 

 P. hucephalus Morch of the Philippine Islands, differs, e. g., in having the ele- 

 vated node of the operculum subcentral, with the margin of the disc elevated 

 and the anterior spine decumbent. 



