HVDROIDA 11 



165 



biological adaptations, which cannot in themselves afford gronnds for distinction of species. How they 

 arise, however, has not yet been thoroughly explained. 



Laomedea flexuosa Alder. 

 1850 Laovicdea flexuosa Alder, Description of three new British Zoophytes p. 440. 



Upright, bnsh\- colonies with inonosiphonic hydrocanlus. Tliere is no thickening of the peri- 

 derm under the apophyses. Branches and stem are zigzag, with a short, ringed iiydrotlieca stalk from 

 the apophyse at each bend. The liydrotheca is as a rule 172 times as long as broad, or hardly as 

 much. In shape it is inversely conical, with sides ver}' slightly curved and quite smooth margin 

 The basal cavity is large, bounded at the top by a distinct diaphragm. The liydrotheca exhibit no 

 unilateral thickening of the wall. 



The gonothecje are carried on short ringed stalks proceeding from the apophyse beside the 

 liydrotheca stalk. They are slenderly conical, as a rule tapering narrowly upward again at tlie distal 

 part, and cut off broadl)' transversely at the distal end, without neck. The gonophores are dimorphous, 

 the males styloid, the female heteromedusoid. 



Material : 



Iceland: Vestinano, on the beach 



Grindavik (depth not stated) 

 Reykjavik ( — - — ) 

 Grafarvogur ( — - — ) 



-n-, 



Laomedea flexuosa is a boreal species characteristic of the tidal zone. On a former occasion 

 (1909 p. 228 footnote) I suggested that the recording of this species from deeper water, down to 60 

 metres depth near Iceland, must be due to confusion with other species. A revision of Sa;munds- 

 s oil's material has entirely confirmed the correctness of this; the specimens he mentions (1902 p. 56) 

 from deeper water are Laomedea geiiieulata (Linne) and Laomedea longissima (Pallas). Sjemunds- 

 son later (1913 p. 78, footnote) quotes in support Levinsen's determinations from the cruises of the 

 "Hauch" (1893); these, however, must be taken with some reserve, and they will probably only 

 be found correct provided they refer to water layers of very low salinity. In fjords with an inter- 

 mixture of fresh water and in inland seas, the limits for the tidal zone w'ill require to be somewhat 

 modified, if it is to correspond with tlie conditions for fauna and flora in the tidal zone of the open sea 

 shore. The deepest-living Laomedea flexuosa are met with out here on the upper Latiiinaria^ which 

 at deepest low water are not infrequently found lying dry; up in the fjords also the upper Laviinaria 

 must be taken as the limit, though they are here only found considerably deeper. Here, however, 

 Lao7iiedea flexuosa rarely goes so far down. The species is, as mentioned, boreal, characterising the 

 tidal zone along the coast of Scandinavia, round the British Isles and at Iceland; it will probably, on 

 further investigation, also prove to be common at the Faroe Islands. In Greenland waters, however, 

 the species seems to be altogether lacking. It does not penetrate into the strictly arctic tracts. 



