438 M. C. Mereschkowsky on new Hydroida 



3. Selaginopsis pacifica^ sp. n, (PI. XVI. figs. 5-7.) 



Trophosome. Hydrocaulus slightly curved, divided into 

 regular internodes. Branches arranged alternately on two 

 sides of the principal stem, two pairs on each internode, 

 divided into five internodes, constricted at the point of attach- 

 ment and at the internodes. Each branch bears one or two, 

 rarely five, secondary branches. Hydrothecje cylindrical, 

 almost entirely immersed in the substance of the axial tube ; 

 aperture oval, with two angles (not teeth) ; hydrothec£e ar- 

 ranged in four regular series, and at the same time in a spiral, 

 the hydrothecEe of each series following one another immedi- 

 ately without leaving any free space or interval. 



Gonosome. Gonangia arranged in two or three series, of an 

 oval form, narrowing gradually towards the base, and truncate 

 at the apex. The surface is ribbed. 



Locality. Metschigman Bay. 



The hydrocauius of this species, in the two specimens pos- 

 sessed by the Academy of Sciences, is not straight, but ele- 

 gantly curved ( PI. XVI. fig. 5), which may be a constant 

 character. The whole colony is of a light greyish-yellow 

 colour, and, owing to the subdivision of the branches into 

 secondary branches, it acquires a tufted character, which, 

 however, is not produced by division in several planes ; on 

 the contrary, both the primary and secondary branches all 

 originate in the same plane. The branches, moreover, be- 

 come gradually shorter as they approach the apex. The 

 branches usually have a strong constriction in the middle, 

 so that the two internodes thus produced are united only 

 by means of a very slender piece. The hydrothecag are 

 always arranged in four regular series (PI. XVI. fig. 6) ; 

 and it is only very rarely that we meet with a small branch 

 having only three series, as in Selaginopsis triserialis. 

 The hydrothecaj are cylindrical, rounded at their posterior 

 part, which is furnished with a small tube to communicate 

 with the cavity of the cylindrical axis. The orifice is oval, 

 furnished with two angles (which, however, are never deve- 

 loped into teeth), and placed at the extremity of a small neck 

 in the form of a very short tube. No two orifices of the four 

 series of hydrothecfe are ever situated at the same level ; in 

 other words, we find a very evident spiral arrangement 

 ai'ound the cylindrical axis, a character which, as will be 

 shown, appears to be common to the whole genus. It must 

 also be remarked that the hydrothecas of each series follow 

 each other almost always without interruption and without 

 leaving any interval ; on the contrary a part of the superior 



