428 THE ANNELIDA POLYCHAETA. 



Of the two pairs of branchiae, the caudal are the smaller and are more ectal 

 in position. Each branchia has a stout trunk which bifurcates almost imme- 

 diately, each branch then bearing several tertiary branches which in turn bear 

 the ultimate filaments directly or, in part, after still farther branching. There 

 is a papilla back of the base of each branchia. 



Nearly always there is a large segmental papilla between the notopodia 

 of the sixth and seventh, and of the seventh and eighth somites, while one may also 

 sometimes be detected on a preceding somite. In one specimen segmental 

 papillae are evident between the processes throughout the thoracic region from 

 the sixth segment caudad. 



There are the usual seventeen setigerous somites. The ventral plates 

 number sixteen or seventeen. The anterior ones are very short, the succeeding 

 ones decreasing in breadth and increasing in length until the last ones are 

 quadrangular or trapeziform, with the length fully equalUng the width. The 

 decrease in width in going caudad is very gradual. 



The setae are finely pointed. Along the distal part is a narrow wing, the 

 edge of which is more or less uneven. The thoracic uncini from the fourth to 

 the seventh somite, inclusive, are arranged in a single series. On the others 

 they are in two completely interlocking series. On the abdomen they are in 

 the usual single series. The abdominal tori are short, but rather high. They 

 are almost equally prominent over most of the length of the abdomen, but 

 toward the caudal end become lower. The uncini above the principal fang 

 have ordinarily but one distinct series of teeth, these numbering usually six, 

 of which the middle ones are distinctly longest and stoutest, the two adjoining 

 ones most commonly of intermediate size but sometimes as large as the 

 middle ones. Occasionally a tooth near the middle of the series is crowded 

 back and reduced in size, and then appears at a distinct level on the apex. The 

 crowding of the teeth may make the series uneven; but there seem never to 

 be truly two series such as occur in bilobata Grube. In profile each uncinus 

 presents on the convex side near its middle a conspicuous, angular protrusion. 

 (Plate 80, fig. 1). 



The caudal end of the body, including about the last eight somites, is 

 abruptly narrowed, the narrowed region decreasing in width gradually caudad 

 and being truncate at the end. The border of the anus is radially folded. (Plate 

 80, fig. 1). 



Locality. (Jalapagos Islands: Chatham Island. 8 January, 1905. Seven 

 specimens. 



