HYDROIDA II 



*35 



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

 ment of the branches, together with an often very marked approach to unilateral arrangement of 

 the hydrothecse. The spirally placed branches are secondarily ramified, often dichotomicallv, but in 

 Sertularia tenera irregularly pinnately. From this then, it is in reality but a short step to HydralU 

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

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

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

 brane in Hydrallmaiiia has a free distal part, whereas in Sertularia, 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- 

 ing between the two genera. 



Hyd rail mania falcata (Linne) Hincks. 



1758 Sertularia falcata, Linne, Systema naturse, Ed. 10, p. 810. 



1868 Hydrallmania falcata, Hincks, A History of the British Hydroid Zoophytes, p. 273, 



Colonies with slender, spiral, monosiphonic and segmented main stem, where 

 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 hydrothecse. Branches and branchlets are segmented, the irregular internodia 

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

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

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

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

 cally. The hydrothecse 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 adcauliue, and has a closing membrane with free distal part. 



The gonotheca; are oval, as a rule somewhat flattened, with a short tubulous 

 neck ; they are quite smooth or irregular and slightly furrowed transversely. 



pi. 58. 

 as a rule each 



Material: 



"Ingolf St. 6 63°43 r N., i^' W., 



- 60 65°oc.' N., i2°27' W., 



- 87 6 5 °o2,3'N., 23*56,2 W., 



- 127 66°33' N„ 2o°05' W, 

 "Thor" 66°ic/ N., 23°27' W., 



65*52' N, 23*58' W, 



64°i6' N., 22°i7' W., 



6 4 °o6' N., 23°i4' W., 



depth 90 fathoms 7,0° 



— 124 0,9° 



— no 



44 5.6° 



— 115 — 120 metres 



62 



50 

 98 



Fig. LXXIII. 

 Hydrallmania 

 falcata from the 

 Trondhjem fjord. 

 Part of a branch 

 of a young, pin- 

 nate colony of the 

 Sertularia-type. 

 (X 40). 



