94 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 25 



the prostomium, much as in Prionospio malmgreni Claparede, and does 

 not form lateral wings as in P. pinnata Ehlers. Prostomial eyes are 

 small, reddish, number 4 in trapezoidal arrangement ; they are all about 

 equal in size, or the anterior are slightly larger and wider apart, located 

 at the midlength of the prostomium, whereas the posterior smaller ones 

 are located between the palpal bases. There is no median antenna. 



The first setigerous segment is biramous, its rami smaller than but 

 similar to those farther back; both notopodia and neuropodia have 

 slender, distally pointed setae. The second segment is larger than the 

 first and carries a pair of smooth, distally tapering branchiae. 



Branchiae number 4 pairs ; the first 3 pairs, located on setigerous 

 segments 2 to 4, are cirriform, increase in size from the first, and the 

 fourth pair is much larger, pinnately divided and terminates distally in 

 a slender end. Typically the branchiae are held so that the 2 of a pair 

 are directed dorsally or somewhat overlap over the middle. 



The postsetal lobe of notopodia is auricular and encompasses the 

 setal fascicle from behind ; this lobe increases in size through the ninth 

 segment and is largest between segments 3 and 6 ; after the twelfth 

 segment it is notably smaller. The corresponding lobes of neuropodia 

 are digitate and taper distally. Parapodia in posterior segments have 

 inconspicuous postsetal lobes. 



The posterior end of the body tapers and ends in a constricted 

 pygidial ring provided with a long, median, filiform cirrus and a pair 

 of much shorter, digitate cirri, arranged in a transverse series. 



Anterior parapodia have conspicuous fascicles of slender, pointed 

 setae. Between segments 11 to 21, a ventralmost, thick, distally pointed, 

 curved seta is present and directed ventro-laterally. Hooded hooks are 

 present from about the thirteenth neuropodium ; at first they occur 

 singly, accompanied by pointed setae ; their number increases gradually 

 so that they form transverse series, accompanied by an inferior fascicle 

 of slender, pointed setae. Seen individually, the hooks have a rounded 

 hood, and the shaft terminates in a thick fang, slightly oblique to the 

 shaft, and a small distal tooth at the upper base of the fang. 



Prionospio pygmaens was at first confused with P. malmgreni (Hart- 

 man, 1955a, p. 77) with which it occurs, and from which it is dis- 

 tinguishable by characters visible under moderately high magnification. 

 It is typically less than half as large as P. malmgreni ; the posterior eyes 

 of the prostomium are never larger than the anterior eyes, and the 

 branchiae of the first pair are cirriform, not pinnately divided. 



