IlYDIiOinA II 



135 



of the point. In the northern Srrtiilaria species, we find a general tendency towards spiral arrange- 

 ment of the branches, together with an often ver\- marked approach to unilateral arrangement of 

 tlie hydrothecse. The spirally placed branches are secondarily ramified, often dichotomically, but in 

 Scrtularia tenera irregularly pinnately. From this then, it is in reality but a short step to Hydrall- 

 mania. And finally, there is a certain amount of variation in the Serfularia species, with regard to 

 proportion between the two sinuses, which in some species ma\- be characterised as of equal size. We 

 have thus, as the last and most essential distinctive feature, the fact that the adcaulinc closing mem- 

 brane in Hydrallniania has a free distal part, whereas in Scrtularia, this is reserved for the abcauline 

 membrane. It may be doubtful whether these small differences should be regarded as of generic im- 

 portance; for the present, however, I have found it most correct to follow Levins en in distinguish- 

 ino- between the two genera. 



Hydrallmania falcata (I^inne) Hincks. 



1758 Sertitlaria falcata, L,inne, Systema naturae, Ed. 10, p. 810. 



1868 Hydrallmania falcata, Hincks, A History of the Britirdi Hydroid Zooplutcs, p. 273, pi. 58. 



Colonics with slender, .spiral, monosiphonic and segmented main stem, where as a rule each 

 internodium bears a branch. The branches form an open spiral about the stem, and 

 are themselves regularly secondarily ramified pinnately; the main stem has a hydro- 

 theca in the corner at the origin of the branch, or may in rare cases be altogether 

 devoid of hydrotheca:. Branches and branchlets are segmented, the irregular internodia 

 bear on the one side (the upper) a more or less close row of hydrothecte, the opening 

 part of which is turned out alternately to either side from the median plane of the 

 branch. On young pinnate colonies the hydrothecce are imbedded, and alternately 

 placed in two opposite rows on the branches, the broad plane of which stands verti- 

 cally. The hydrotheca; are bottle-shaped to tubular, distally often bent, in young colo- 

 nies with biserial arrangement, somewhat imbedded, in older ones with unilateral ar- 

 rangement and almost sessile. The opening margin is armed with two large lateral 

 teeth, the largest sinus is adcauline, and has a closing membrane with free distal part. 



Kg. LXXIIl. 

 Hyiiralhuan in 



falcata from the 



The gonothecce are oval, as a rule somewhat flattened, with a short tubulous Trondhjem fjord. 



1 • 1 . 1 r J i. 1 I'art of a branch 



neck ; they are quite smooth or nregular and slightly furrowed transversely. ^^ ^ voung, pin- 



nate colony of the 

 Material: Sertularia-ty^e. 



(X 40)- 



"Ingolf" St. 6 63°43' N., i4°34' W., 



— - 60 65='09' N., 12=27' W., 

 _ - 87 65°02,3'N., 23°56,2W., 



— - 127 66°33' N., 2o°05' W., 

 "Thor" 66°i9' N., 23=27' W., 



65^52' N., 23^^58' W., 



— 64°i6' N., 22°i7' W.. 



— 64°o6' N., 23' 1 4' W., 



depth 90 fathoms 7,0" 



— 124 - 0,9° 



— no — — 



— 44 — 5,6° 



— 115 — 120 metres 



— 62 — 



— 50 — 

 98 - 



