ANATOMY OF ARRNICOLA ASSIMTLTS. 755 



than any of the others, and its fellow on the left side is 

 represented by a single filament about half a millimetre iu 

 length and bifid at the tip. In the Macquarie specimen 

 there are only twelve pairs of gills, the first being well 

 developed and situated on the eighth ehfetigerous annuliis. 

 The true first gill ^ is totally absent, a condition frequently 

 met with in A. marina. The gills of the Otago specimens 

 are of the pinnate type, and are beautifully regular in 

 arrangement. Each consists of fourteen to sixteen main 

 stems, usually 3'5 — 4 mm. long (but in several cases reaching 

 G mm.), which radiate from the base of the notopodium, and 

 are connected near their bases by a web-like membrane. 

 Each stem bears eleven to eighteen pairs of pinnfe, which are 

 either opposite or almost alternate in arrangement and 

 usually divide dichotomously. These gills are remarkable 

 for the enormous size of tlie afferent and efferent blood- 

 vessels, best seen in the main stems and in the larger 

 pinufe. They closely resemble the gills of the Laminarian 

 variety of A. marina figured by Gamble and Ash worth 

 (1898, pi. i, fig. 2), except that the webbing at the base is 

 more pronounced in the southern specimens. The gills of 

 the Macquarie specimen are of a different type. They have 

 only seven or eight main trunks 3"o — 5'5 mm. long, each 

 bearing six or eight pinna) on each side, and these are less 

 regularly arranged than in the Otago specimens. There is 

 no connecting membrane at the bases of the main trnnks. 

 These gills resemble in form, but are larger than, those of the 

 Uschuaia specimens of A. assimilis (see p. 740). 



The annulation of the skin is exactly like that of A. 

 assimilis (see p. 741). 



Setee. — The notopodial setae (figs. 2, 2 a) taper more 

 abruptly at the tip than those of A. assimilis. Those of 

 the Otago specimen ai-e 4 mm. long. The usual pointed 

 barbs or processes are present on one side of the shaft of the 

 seta, while on the other is a well-marked lamina, which 

 in most seta? is 12 fx, and in some is 15 /n broad. The 



The pair of effereut vessels of this segment is also completely suppressed. 



