448 M. C. Mereschkowskj on new Hydroida 



larly bent, with regular internodes, destitute of branclies to the 

 apex, where the width of the axial tube suddenly diminishes 

 considerably, and it at the same time gives origin to branches. 

 Branches divided into internodes, rather short, issuing from 

 all sides of the principal stem, one from each of its internodes, 

 ramified in their turn so that each branch -internode gives off 

 a secondary branch, which is divided once or twice ; and all 

 these secondary branches are turned towards the axis of the 

 colony (inwards). Hydrothec^ tubular, a little contracted at 

 the extremity ; aperture broad oval, furnished with two large 

 teeth arranged unsymmetrically ; arrangement of the hydro- 

 thecse, although biserial, not in the same plane, having at the 

 first glance the appearance ofheing uniserial. 



Gonosome unknown. 



Locality. Unalaschka [M. Petelin, 1847). 



The hydrorhiza is formed by the agglomeration of hydro- 

 phytons so interlaced and bound together as to form a con- 

 tinuous layer of a dark brown colour, which gives origin to 

 more than thirty colonies placed very close to each other. 

 The hydrocauli, of a rather dark brown, are straight, not an- 

 gularly bent, slightly and irregularly waved, cylindrical, and 

 nearly of the same thickness throughout their length, except 

 the extremity, which decreases very abruptly in diameter. 

 The whole has very much the character of a colony of Tuhu- 

 laria indivisa (PL XVII. fig. 20). The whole stem is divided 

 into regular internodes from 2 to 5 millims. long ; and in all 

 the brown part of the stem it is entirely destitute of branches. 

 Only the upper part, the extremity, which abruptly becomes 

 more slender, more delicate, and, at the same time, entirely 

 colourless, begins to give origin to branches, which are also 

 excessively delicate and entirely colourless. A long brown 

 and rigid stem, having at its extremity a thick tuft of small, 

 very delicate, and flexible branches, presents a very singular 

 and unusual appearance. It sometimes happens that the 

 principal stem bears one or a few small colourless branches 

 about the middle or in the upper third j but this case is rare 

 and exceptional. 



The upper part of the stem is divided, like all the rest, into 

 internodes ; but these are shorter, and each of them gives 

 origin to a single branch. The arrangement of the branches 

 is spiral ; that is to say, they spring from all sides. The 

 branches, which are divided, like the principal stem, into regu- 

 lar internodes, are also divided into secondary branches, each 

 internode giving origin to a single secondary branch, which 

 is always turned towards the interior of the colony, so that the 

 side of the primary branch turned towards the exterior of the 



