172 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



make out just what the peculiarities of commensals are, 

 they are so slight and indeterminate. Commensals are not, 

 as in P. drevisetosa, decidedly more pigmented; but, on the 

 contrary, are usually somewhat paler than the free-living 

 individuals. The elytra are a trifle thinner and smoother. 

 There is no special modification of the sets, or of the body- 

 form. 



The largest and finest specimens have been collected at 

 San Pedro, where the species is very abundant on rocky 

 shores near low-water mark. It is probable that this por- 

 tion of the California coast is its " metropolis," for the indi- 

 viduals obtained in San Diego Bay (where it occurs in some 

 abundance on the piles) and at Pacific Grove are very 

 much smaller than the general run of specimens from San 

 Pedro. It should, however, be stated that most 1 , if not all, 

 of the very large individuals collected at San Pedro were 

 commensalistic in the tubes of a huge Amphitrite common 

 in that region, but not found, so far as present knowledge 

 goes, at San Diego or at Pacific Grove. 



In addition to the localities above mentioned, this species 

 has been collected by Mr. H. B. Torrey at Avalon, Santa 

 Catalina Island, and on San Clemente Island. 



At Pacific Grove the breeding season is evidently in the 

 summer. A female collected there in July shed ripe eggs. 



Polynoe gigas, sp. nov. 

 Plate VII, Figs. 33, 42, 42a; Plate VIII, Figs. 48, 48a, \%b, 49. 



Form much elongated, robust when fully grown, obtusely rounded at both 

 ends. Young much more slender proportionally and gradually tapering 

 from the middle to the posterior extremity. 



Somites variable in number, usually between eighty and ninety; elytra like- 

 wise variable, forty to fifty pairs. Elytra not extending to posterior extremity. 

 Anus conspicuous, at anterior edge of penultimate somite. 



Prostomium (fig. 33) very broad, globose, median fissure slight, reaching 

 not over half-way to base of prostomium. Eyes four, anterior pair situated 

 at widest part of prostomium, much larger than posterior pair, which are 

 nearer together. Antennae attached at level of tentacle, articulated on anterior 

 prolongations of cephalic lobe. 



1 My notes are unfortunately defective on this point; but certainly a considerable pro- 

 portion of the largest individuals were commensal with Amphitrite. 



