POLYCH^TA OF THE FAMILIES SERPULID^ AND SABELLID^. 357 



The thorax has eight setigerous segments, the abdomen 52 ; the posterior abdominal 

 seo-ments are much shorter antero-posteriorly, and rather wider than the front ones. 

 The gill rachises are nearly 1 mm. in diameter and very nearly cylindrical ; in some 

 cases they end in a small finger-like process, but the thin straggling pinnae extend at 

 irregular intervals nearly up to this end. There are sixteen on the left and fifteen 

 on the right, the four ventral ones on each side being much smaller. To the most 

 ventral one on each side is attached the membrane which, just below, enlarges greatly 

 and forms a kind of pocket on each side ; the membranes then approach one another 

 and join together at the posterior end of the fissure between the ventro-lateral lobes 

 of the collar. 



From the dorsal aspect there is great resemblance to Ehlers' P. spathiferus (4, 

 p. 278), the collars of both species being similar. 



The first segment has no torus, and its setae are of one kind only, similar to the 

 superior ones of the other segments (fig. 7, g). 



December 23, 1912. 



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