312 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 7 



thus not as in most species of Polydora where they are usually much 

 reduced in size and number. The heavy spines are of 2 kinds — a larger 

 anterior row of about 5 or 6, with a heavy cylindrical stem and an 

 expanded, bushy top (pi. 45, fig. 12), accompanied by an equal number 

 of smaller spines with weaker stem and weakly bifid, hooded top beset 

 with short bristles (pi. 45, fig. 13). 



Branchiae, first present from the seventh setiger, are continued 

 through about 50 to 70 segments, but absent from about the posterior 

 two thirds of the body. They are broad, straplike, those of opposite sides 

 directed inward and backward, not quite touching medially (preserved). 

 Hooded hooks are first present in the tenth neuropodium ; here there are 

 about 5 hooks medially, accompanied with capillary setae above and 

 below. By the twelfth there are about 8 such hooks with only 1 or 2 

 capillaries. Hooded hooks in anterior parapodia have a bifid tip, the distal 

 end at an oblique angle to the main stalk. In middle and posterior seg- 

 ments these are gradually replaced by hooded setae that are distally 

 pointed (pi. 45, fig. 14). In a posterior segment there are about 12 such 

 hooded setae; when their tips are broken off they somewhat resemble 

 irregular hooks, but their incomplete condition may be checked by an 

 examination of their hood, which extends far beyond the broken tip 

 (pi. 45, fig. 15) or by comparison with others in the same fascicle (com- 

 pare pi. 45, figs. 14, 15 ). In so far as I am aware, this is the only described 

 species of Polydora with such hooded setae. Another aberrant feature is 

 the pygidium — here provided with 4 subequal clavate papillae, disposed 

 in a cross, instead of a flaring or disklike membrane (pi. 45, fig. 11). 



The eggs are white, laid singly within the tube where the young 

 develop. No stage later than a 3-segmented was observed. This is a typical 

 spionid chaetiger; the long provisional setae of the first 3 segments 

 extend well beyond the pygidial region (pi. 45, fig. 16) ; prototroch and 

 telotroch are developed. This stage is colorless save for 4 black eyes and 

 a dark alimentary tract. 



P. citrona differs from other species of the genus in having a minute 

 prostomial ridge, in having modified spines of 2 kinds, both with bristled 

 tops, in having its posterior hooded neurosetae terminate in a point, and 

 in having pygidium provided with 4 cirri. It has been found only in 

 Mission Bay, near the Causeway, during September, 1938, in beds of 

 Upogebia, but was probably not commensal. 



Holotype. — AHF no. 33. 



Type locality. — Mission Bay, California. 



