from the North Pacific Ocean. 



443 



into two, and each half bear at its extremity a fresh series of 

 branches, a new colony. The hydrothecte are arranged in 

 ten regular series ; but this character is not perfectly constant ; 

 sometimes, although rarely, we meet with very slender 

 branches which have only seven or eight series ; and, further, 

 the number ten appears to be most constant at the ends of the 

 branches, where it is almost always met with ; whilst towards 

 the point of attachment the number very often diminishes, 

 becoming nine, eight, and sometimes seven, or even six. The 

 great number of series causes the branches to be very thick ; 

 in this species they attain the greatest thickness that I 

 know. 



The hydrothecse are arranged so as to form not only longi- 

 tudinal series, but also a very regular spiral line around the axis 

 (PI. XVII. fig. 15). This character is not the exclusive pecu- 



Fic 



Fie 



Fk. 1. 



c: 



f^ 



1st , 

 series. 





/'uj'' 



o 



'^: 



2nd series. 



Biserial type. 



2nd series. 3rd series. 



Type luultiserial 

 by displacement. 



Type multiseiial 

 by torsion. 



liarity of Selaginopsis decemserialis, but, as we have already 

 seen, it belongs also to the other species that I have described ; 

 throughout we have found that no two orifices of the more or 

 less numerous seines ever come at the same level. This spiral 

 arrangement, which, as I believe, iscommon to the whole genus, 

 renders it possible to attempt an explanation of the polyserial 

 type, not by means of the displacement of the hydrothecse of 

 each series in the biserial type (that is to say, by the divi- 

 sion of each series into two, three &c.), but simply by the 

 torsion of the axial tube, which would produce a spiral and, 



