442 M. C. Mereschkowsky on 7ieiv Hydroida 



neither in S. hidentata and ochotensis, nor in any other species 

 belonging to the genus, do we ever see a truly verticillate 

 arrangement (we can observe only an arrangement in lon- 

 gitudinal series and in a spiral) ; on the contrary, it may be 

 asserted of this genus that no orifice of a hydrotheca is ever 

 placed at the same level as another. 



6. Selaginopsis decemserialisj sp. n. (PI. XVII. figs. 13-16.) 



Trophosome. Hydrocaulus straight, cylindrical, very thick, 

 angularly bent, divided into internodes. Branches springing 

 from all sides by three together, dividing at the very point of 

 their attachment, united with the stem by means of a little 

 tube; straight, simple, cylindrical, becoming shorter towards 

 the apex. liydrothec^e large, cylindrical, with an oval aper- 

 ture, entirely immersed in the substance of the axiaFtube, ar- 

 ranged in ten regular longitudinal series, and forming at the 

 same time a spiral round the axis. 



Gonosome. Gonangia arranged in several longitudinal 

 series, more or less cylindrical, narrowed at the base, and 

 furnished with a wide and short cylindrical elevation at the 

 apex, most frequently turned inwards. 



Locality. Northern Pacific Ocean (shore of Pallana, M. 

 Wosnessensky, 1849). 



This interesting species belongs to the type of Selaginopsis 

 affecting more or less the general aspect of Thujaria thuja. 

 In S. decemserialis this habit is exactly reproduced, especially 

 in a variety of the species which I have figured PI. XVII. 

 fig. 13. This variety diflfers from the normal type by its 

 branches being shorter, and not diminishing as they advance 

 towards the apex, which is also the case in Thujaria thuja^ 

 and causes the general form of the colony to be cylindrical ; 

 whilst the normal form has the apical branches only one half 

 or one third the length of the lower ones, although of the same 

 thickness, producing a general conical form of the colony. 

 The hydrocaulus is long and destitute of branches for the 

 greater part of its length (just as in Thujaria thuja) ; it is 

 angular ; and each angle bears a short but wide tube, which 

 serves as a base for three united branches. The mode of 

 ramification of the branches is very consistent in the difl^erent 

 species. As we have seen, in Selaginopsis thuja and S. ocho- 

 tensis the branches subdivide into six parts, and not from their 

 actual point of attachment, but at a certain distance therefrom ; 

 while here there are always only three small branches, and 

 they unite at the very point of their attachment (PI. XVII. 

 fig. 14). 



Sometimes in this species we see the principal stem divide 



