WEST COAST HYDROIDS 75 



branches, but often only two. The branches are not nearly so 

 coarse as the main stem, they are silvery white in appearance, 

 while the stem is much darker. Only occasionally is there any di- 

 vision into internodes. The h'ydrothecae are closely crowded, es- 

 pecially on the branches, so much so that in many instances the 

 upper point where the one hydrotheca leaves the branch is on a 

 level with the next hydrotheca in order. Those on opposite sides 

 alternate quite regularly. Both borders of the hydrotheca are 

 regularly curved, but the inner, upper border is much longer 

 than the outer lower one, so that the even margin of the nearly 

 circular aperture is placed parallel to the axis of the branch, 

 an exception to the general rule among Thuiarian forms. The 

 hydrotheca is largely immersed, seldom more than one-fourth 

 being free. The operculum consists of a single abcauline flap. 



Gonosome. — Unknown. 



Distribution. — San Juan Archipelago, in both Prof. Kincaid's 

 and Mr. H. Moon's collection. 



Jaderholm^'^ has described and figured a species, Thuiaria 

 Jcolaensis, which bears a great resemblance to this species. In 

 T. kolaensis, however, the branches are turned with the flat side 

 upward, a condition which is sufficiently unusual to be of specific 

 value, and they are usually dichotomously branched near the tip. 

 The branches of T. aiha lie in the same plane as the stem and 

 show no indication of any tendency to dichotomous branching 

 near the tip. Apart from these features, the same description 

 seems to apply to the two. 



THUIAEIA AEGEXTEA (Lmnteus) 



SertuJaria argentea Lixx^us, Svstema Xaturfe, 175S, p. 809. 

 Sertidaria argentea Clark, Hydroids of the Pacific Coast, 1876. p. 257. 

 Thuiaria argentea Xuttixg, Hydroids from Alaska and Puget Sound, 1899, 

 p. 741. 



Thuiaria argenta Xuttixg, Hydroids of the Harriman Ex., 1901, p. 184. 

 Sertularia argentea Torrey, Hydroida of the Pacific Coast, 1902, p. 67. 

 Thuiaria argentea Xuttixg, American Hydroids, Part II. 1904, p. 71. 



Distribution. — One of the commonest species in shallow water 

 off the Alaskan Coast (Nutting) ; San Juan Achipelago. 



THUIAEIA DALLI Xutting 

 Sertularia ntpressoides Clark, Alaskan Hydroids, 1876, p. 220. 



5" Xorthern and Arctic Invertebrates, Part IV, 1909, p. 88, Figs. 17-18, 

 Taf. YIII. 



