458 THE ANNELIDA POLYCHAETA. 



little less than this. At the distal end it is completely encircled by a crowded 

 series of elevated tubercles with scarred distal ends which are apparently the 

 bases of lost tentacles. The entire surface between this ring and the proximal 

 end is covered with numerous, but well-separated, scars representing places of 

 attachment of tentacles that have been lost, together with some long, cyhndrical, 

 or filamentous, tentacles still in place. On the dorsal side just back of the 

 tentacuhferous region there is an elevated transverse fold which is divided by 

 a transverse furrow, and the anterior margin of which is semicircular; on the 

 middle part of this fold is a more elevated, transversely oblong, area which in 

 front is bicornuate, the two thick processes anteriorly rounded, extending for- 

 ward across the first division of the lobe. Caudad of this lobe, extending be- 

 tween its caudal ends, is a straight, transverse, thick fold, which is longer across 

 its ends than mesally, and the surface of which is essentially smooth Uke that of 

 the first ridge. Behind these ridges are two very short, achaetous, complete 

 rings. The ventral region of the first of these is thickened and conspicuously 

 elevated beyond the level of the second one; it projects forward so that its length 

 is more than twice that of the second ring. 



The succeeding rings to the end of the thorax are setigerous. Of these 

 the first three are very short both above and below. The fourth is very short 

 ventrally, but dorsally is much longer than the preceding ones. The following 

 somites are not separated above by distinct intersegmental sulci, but ventrally 

 the sulci are distinct and the somites long. Each has a broadly elevated, 

 whitish, anterior region, which may be obscurely divided by a weak transverse 

 furrow and a depressed posterior region. Each is crossed by the distinct neural 

 furrow, which is particularly deep on the posterior part of the somite. 



The branchiae are present on the first three setigerous somites, a pair on 

 each; on each side they arise just above the notopodia. They are very thick, 

 smooth filaments, pointed at the distal end. 



The first four pairs of notopodia are much smaller than the others, the first 

 being smallest of all and appearing as mere tubercles, with setae correspondingly 

 short. The other neuropodia are moderately stout, cyhndrical and long, the 

 length equalling or somewhat exceeding that of the somite ventrally. Dis- 

 tally they are narrowed subconically, and the tip is somewhat compressed in 

 the subanterocaudal direction. On the ventral side, at the distal end near the 

 end of the series of setae, is a slight conical tubercle. The uncinigerous tori 

 begin on the fifth setigerous somite. Each torus is a flattened structure with the 

 distal end, along which the uncini are arranged, straight; constricted at the base 



