238 BUSH 



The thoracic setae vary in the three segments. All the inferior ones 

 are of the usual slender capillary form ; the superior ones of the collar 

 fascicle have a conspicuous, fin-like, posterior expansion and long, nar- 

 rower, gradually tapered, coarsely serrate, terminal portion; those of 

 the other fascicles have a broad, smooth, tapered blade, a few in the 

 third fascicle with odd comb-like ends. Uncini rather broad, with two 

 rows of minute teeth. 



Posterior segments much swollen, bearing conspicuous bunches of 

 mucous glands nearly concealing the two setae, both of which at first 

 have broad pennant-like blades, but farther back one has the shaft 

 simply pointed and curved. 



Strings of undeveloped eggs were in many of the tubes. 



Common at Dutch Harbor, on rocks and stones ; rare in Prince 

 William Sound, at Orca, on tubes of Serpula splendens ; and also at 

 Sitka, on shells and tubes of Crucigera zygophora. 



SPIRORBIS VARIABILIS sp. nov. 



pi. xxix, fig. 3, a; rl. xxxix, figs. 24, 25 ; pi. XL, fig. 4; pi. XLIII, fig. 16; 

 pi. XLIV, fig. 17. 



Type locality. Sitka Harbor. 



Tube thick, vitreous, usually semitransparent, sinistral, the few 

 whorls spreading over one another, usually forming a low spire with 

 or without a small central cavity, the top spirally grooved, the grooves 

 in some instances indicated only by the fine sinuous striae of growth 

 and a slightly raised interspace, in others very deep, with three broad, 

 rounded ridges forming conspicuous notches and tooth-like projections 

 in the margin of the aperture, the margin in the other form being un- 

 interrupted. There is great variation in the manner of coiling, some 

 specimens assuming a form that can be distinguished from semiden- 

 tatus only by its smaller size and opposite coil ; others resemble viola- 

 ceus but turn in the opposite direction. 



Diameter 2-2.5 mm ' 5 height 1-1.5 mm. 



Animal not differing essentially in number of segments, branchiae, 

 and form of operculum from S. semidentatus . Some opercula have 

 two saucer-shaped calcareous plates, which can be readily separated. 



Strings of eggs were found along the back of the posterior segments. 



Attached to rocks and fragments of shells, either singly or in small 

 colonies. 



