26 HYDROIDS COLLECTED BY THE " HUXLEY " FEOM 



Through the kindness of Mr. E. Kirkpatrick, I have examined at 

 the British Museum the specimen of Lidonila halccioidcs from Torres 

 Straits. It is not like Zafoea ^nnnata, and it is not like Allman's 

 figure of Lafoea halecioides from the Faeroe Channel. 



Pictet and Bedot record the occurrence of Lidordla halecioides in 

 the Bay of Biscay. Their description and beautiful figures show that 

 they refer to the form originally described by Allman from the 

 Faeroe Channel. 



The distinction between the two genera Lafoea and Lictorella rests 

 entirely upon the structure of their hydrothecne. In Lafoea the cavity of 

 the hydrotheca is directly continuous with that of the stem or peduncle, 

 but in Lictorella the cavity is distinctly differentiated from that of the 

 peduncle. 



In the lower part of the hydrotheca of Lafoea pinnata there is a fine 

 transverse circular line on the inner side of the perisarc. The line is 

 more readily seen when the hydrotheca are empty, and, better still, 

 when the perisarc has been lightly stained. Two circular lines, close 

 together, are not uncommon, and occasionally a hydrotheca was seen 

 without a circular line. In mounted specimens one usually sees this 

 line and nothing more, but occasionally in an empty hydrotheca a 

 very fine membrane, with a central hole, was found stretching across 

 the hydrotheca. The circular line is a very slight thickening of the 

 perisarc, to which this membrane is attached. When the colony 

 is alive the membrane extends from the body of the hydranth to the 

 perisarc of the hydrotheca, and shuts off the lower part of the 

 liydrotheca from the exterior. The membrane is so thin and delicate 

 that it usually disappears on the death or absorption of the hydranth. 

 Levinsen (1893) has noticed a similar membrane in Lafoea fruticosa. 

 This membrane has commonly been called a diaphragm and considered 

 homologous with the diaphragm of a typical Campanularian Hydroid. 

 To compare this delicate membrane with the firm perisarcal diaphragm 

 which forms the bottom of the hydrotheca of a Campanularia is likely 

 to cause confusion. The membrane is not at the bottom of the 

 hydrotheca, and it does not, on account of its pliability, in any way limit 

 the contracting back of the hydranth; when the hydranth of a Lafoea 

 is contracted back it does not rest upon the diaphragm like a Cam- 

 imnularia, but contracts back below the diaphragm to the bottom of 

 the hydrotheca. 



Lietorclla halecioides horn Torres Straits has a typical Campanularian 

 diaphragm. Its hydrotheca, with a thick basal wall, is upon a short 

 peduncle, and the cavity of the hydrotheca is distinctly differentiated 

 from that of the peduncle. 



Description of Lafoea pinnata. This Hydroid has two modes of 



