J J. HYDROIDA 11 



Diphasia alata Hincks. 

 1855 Sertnlaria alata, Hincks, Notes on British Zoophytes, p. 127, pi. 2. 

 1868 Diphasia alafa, Hincks, A History of the British Hydroid Zoophytes, p. 258, pi. 48, fig. 2. 



Upright pinnate colonies with a not ver\- marked, brown, nionosiphonic stem, exceptionally 

 polysiphonic in its basal part; the stem and branches are indistinctly segmented. The hydrothecse 

 are arranged in opposite or subalternate pairs; they may also, in exceptional cases, be alternately set. 

 On the branches, the hydrotheca; exhibit a tendency towards nnilateral arrangement on the front of 

 the colon\-. The branches arise alternately from the stem; between two snccessive branches on the 

 same side of the stem there are three hydrothecae, the lowest at the branch corner. The hydrothecae 

 are large, bent to an angle, with a free distal portion of the adcanline wall between one-third and 

 one-half the length of the hydrotheca, abont eqnal to the opening diameter. The abcanline wall has 

 at the middle, near the bend, a prominent transverse inner rib; the angle between the branch axis 

 and that of the distal part of the Indrotheca is greater than 60''. The plane of the hydrotheca aper- 

 tnre is almost perpendicnlar to the branch axis; the margin lias a deep adcanline sinus, in which the 

 large opercular plate is attached. 



The gonothecie are small, almost laear-shaped, distally quadrilateral in section, with a short 

 and blunt distal point in each corner, and a small round distally central opening, but no neck. The 

 female gonothecse develop no brood-chamber; they are as a rule slightly asymmetrical, whereas the 

 males are symmetrical in structure. 



Material : 



"Thor" 35^57' N., ~,°y^' W., depth 740 metres. 



Diphasia alafa belongs to the warmer tracts of the eastern part of the Atlantic, and seems 

 there to be mainly restricted to the lower part of the littoral region and the upper portion of the 

 abyssal. It is a rare vi.sitor in the northern waters, where it has been observed off the west coast of 

 Scotland, at the Hebrides, Shetland, and the west coast of Norway from Jteren to a little north of 

 Bergen. It lias not, however, been recorded from the Faroe Islands, Iceland or Greenland. 



Gen. Dynamena (Lamouroux). 



Upright colonies with imbedded, bilaterally built hydrothecse. The hydrotheca aperture has 

 two large lateral teeth, between which there is a large abcanline sinus and a smaller adcanline one; 

 the latter is often divided into two b\- a slightly prominent median tooth. In each main sinus a mem- 

 brane is fixed, so that the closing a])paratiis consists of two membranes, the abcanline with a free 

 distal part. The lK)lyp has no ])roiiouiiced blind sack. 



This definition of the genus Dyiiainriia we also find indicated by Kiihn (1913 p. 252). Levin- 

 sen is not dispo.sed to consider the development of a pronounced blind sack as of any systematic 

 importance (1913 p. 286), which view must doubtless be accounted for by his having apparently con- 

 fn.sed this feature in the organisation with casual vS-shaped hydraiith contractions. Kiihn regards the 



