froDi tJie North Pacific Ocean. 449 



colony is always destitute of branches (PI. XVII. fig. 22 *). 

 There are usually eight or ten secondary branches (fig. 22, c), 

 which are either simple or divided, usually once, rarely twice. 

 At the same time the secondary branches are not placed in 

 the same plane. All this division and subdivision, which is 

 very complicated in our species, is the more difficult to see, 

 because the branches, owing to their flexibility, curve and 

 interlace to form a dense tuft. The hydrothecaj (PI. XVII. 

 fig. 21) are cylindrical, a little compressed at the extremity, 

 a little inflated at the base, furnished with a wide aperture 

 with its margin armed with two long teeth, which are not 

 placed exactly opposite to each other. Their position is 

 exactly analogous to that of the hydrothecse in SertuJarella 

 pinnata, S. F. Clarke ; that is to say, although biserial, they 

 are not placed in one and the same plane, but '^ inclining 

 towards each other, so that in a general view they appear to 

 be aiTanged uniserially (PI. XVII. fig. 21). The hydrothecaj 

 on the secondary branches are arranged alternately." 



Length of the largest colony 80 millims. ; length of the 

 colourless part divided into branches about 15 ; length of 

 hydrothec^ 0"37, maximum breadth 0*1 6. 



This curious species of Sertularella differs strikingly from 

 all other known species by the general form of the colony, 

 the mode of ramification, the bidentate hydrothecse, and espe- 

 cially by the singular manner in which these are arranged 

 upon the branches, affecting a uniserial arrangement. By 

 this last character this species very distinctly approaches Ser- 

 tularella pinnata, Clarke, the finest species that I know, 

 Sertularella Clarhii^ however, is distinguished from this by 

 the absence of the plumose character of the colony (which 

 renders S. pinnata so pretty), as well as by the presence of 

 only two instead of three teeth. The arrangement of the 

 hydrothecEe in both species has some analogy with that 

 occurring in Hydrallmania falcata and in the genus Desmo~ 

 scyphus f. 



There are in the collection of the Academy more than 

 twenty magnificent specimens of this hydroid united upon a 

 common layer of hydrorhiza, brought from Unalaschka. 



I give this species its specific name in honour of the Ame- 

 rican zoologist S. F. Clarke, author of several excellent works 

 on the Hydroids of America. 



* This figure only repi-esents the mode of ramification, in the species in 

 question, dfagrammatically. 



t Allman, Journ. Linn. Soc. vol. xii. (1876), p. 264, pi, xiv. figs. 3-7, 



Ann. db Mag. N. Hist, Ser. 5. Vol. ii. 30 



