HYDROIDA II ^5 



Thujaria alternitheca is probably an arctic species of highly localised occurrence. It belongs 

 to the deepest littoral waters. Previously, it was only known from Davis Strait, but is now found to 

 occur also off the west coast of Iceland, where it has been confused with a form of much finer build, 

 Thujaria lonchitis. 



Thujaria variabilis nov. nom. 

 1899 Selagiuopsis arctica, Bonnevie, Den Norske Nordhavs-Expedition, p. 87, pi. 6, fig. 4. 



Coarse, upright pinnate colonies with undivided branches. The stem is slightly zigzag, divided 

 into internodia of irregular length, with from two to twelve regularly alternating branches and two 

 single rows of hydrothecse; the stem is not spirally coiled. The stem has from two to four, normally 

 three, hydrothecse between two successive branches on the same side, the lowest in the branch angle. 

 The branches have four, exceptionally two or three, rows of hydrothecae; on the four-rowed branches, 

 the hydrothecse are set in opposite pairs, the symmetrical plane of the one pair being then perpendi- 

 cular to that of the next; three-rowed branches are spirally coiled, two-rowed straight, with the sym- 

 metrical plane of the hydrothecae vertical. The hydrothecae are broad and deeply imbedded, with a 

 short, often quite insignificant free distal part of the adcauline wall, never more than a third of the 

 opening diameter, or one-tenth to one-twelfth the length of the hydrotheca. The opening is round, 

 with smooth margin, without teeth or sinus, and has a large opercular plate abcaulinally fixed. 



The gonothecae are set on the upper side of the branches, and proceed from close below the 

 base of the hydrothecae. The gonothecae are inversely conical, distally cut off transversely, without neck. 



Material: 



Iceland, Reydarfjord, depth 80 fathoms (some of them labelled Thujaria lonchitis). 



A number of very fine colonies belonging to this species have been incorrectly determined 

 by Ssemundsson as Thujaria lonchitis, from which Thujaria variabilis is immediately distinguish- 

 able by its extremely robust appearance and thick branches. The colonies are interesting in several 

 respects. They show, in the first place, that aberrant branches with fewer than four hydrothecae rows are 

 by no means rare, and in the second, that the number of hydrothecse rows on a branch may vary 

 from one internodium to another. There are thus some branches which are basally quadriserial, 

 distally bi- or triserial; others again are biserial, triserial or quadriserial throughout their entire length, 

 or only quadriserial at the extremities. This feature, then, is subject to great variation. It is also 

 remarkable that biserial branches are straight, whereas the triserial, and exceptionally also the qua- 

 driserial, are twisted, so that the hydrothecse here lie in very steeply ascendant spiral tiers about the 

 branches. The normal quadriserial branch on the other hand, presents a compressed Staurotheca type, 

 where the single hydrotheca pair is revolved as against the preceding pair, and has its plane of 

 symmetry perpendicular to that of the latter; this also gives very close spiral lines in the arrange- 

 ment of the hydrothecse, as pointed out by previous investigators. The species, with its variations, 

 gives a drastic exposure of the value attaching to the distinctive characters for the genera Stauro- 

 theca and Selagiuopsis. 



It is evident from the foregoing that Selaginopsis artica Bonnevie must be classed under the 



The [ngolf-Expedition. V. 7. 19 



