426 THE ANNELIDA POLYCHAETA. 



exclusive of the tentacles, has a length of near 55 mm., with a maximum width 

 of 3.9 or 4 mm., which is at the twelfth somite. From there the body narrows 

 cephalad and more decidedly caudad, the thorax passing gradually into the 

 abdomen, which at its beginning has a diameter of 2 nun. and narrows gradually 

 from near its middle to the more abruptly narrowed caudal tip. The widest 

 level in the thorax is farther caudad than in galapagensis with the narrowing 

 cephalad more gradual. The type consists of about one hundred and twenty- 

 eight somites. 



The prostomium bears numerous tentacles above and laterally which are 

 proportionately shorter and somewhat finer than in galapagensis. The tentacles 

 are transversely banded with numerous fine brown lines, these in the paratype 

 less marked than in the type. 



The peristomium forms a prominent lower lip, of which the distal edge is 

 straight. 



On each side a lateral membranous fold arises on the third somite as in 

 related forms; line of attachment straight, not crossing to the second somite as 

 it does in galapagensis, etc. The fold is transversely elongate and is abruptly 

 shorter from the middle to the mesal end. It is crossed longitudinally by many 

 fine white veins or lines. (Plate 79, fig. 12). 



The branchiae are smaller than in galapagensis. The filaments are similarly 

 numerous. 



There are seventeen setigerous somites. 



The ventral plates are sixteen or seventeen in number. Together they 

 form a narrow area which narrows acutely caudad. The plates are relatively 

 very narrow, the plate of the twelfth somite being only 1 to 1.2 mm. wide, while 

 the total width of this somite is 4 mm. In galapagensis the ventral plates are 

 relatively decidedly wider, the plate of the twelfth somite being 2.7 mm. wide in 

 a specimen in which that somite has a total width of 5.2 mm. 



The thoracic uncini are uniseriate on somites V to VII inclusive. On the 

 others they are in two interlocking series, in one of which they are progressive 

 and in the other regressive. 



The uncini are decidedly smaller than in galapagensis, the prominence on 

 the convex edge is clearly less pronounced, and the prominence on the opposite 

 edge is relatively farther from the base of the large tooth. The small teeth 

 above the base of the large one are arranged very clearly in two rows, the median 

 tooth of the first of these series being large. (Plate 79, fig. 13). 



The caudal tip of the abdomen is strongly narrowed, the tip as seen from 



