A COLLEOTIUN OF HYDROIDS. 



273 



account of the structure and variability of Alder's hydroid, it 

 is not possible to refer it to this species with any certainty. 



The hydroid grows on the surface of sea-weed, and may 

 extend over a very considerable area. In all the specimens 

 obtained the hydrocaulus has exhibited vexy little branching, 

 and the total height has not exceeded about ^ in. 



The polyps are of a very pale horn colour. 



Text-fig. 1. 



sx/^. 



Eudendrium piirvum, sp. n. 



Trophosome. — The h y d r o r h i z a or creeping stolon branches 

 in an irregular manner, and may form a more or less com- 

 plicated network. The diameter is about O'lo mm., and the 

 thickness of the perisarc 4"4 fx. 



Hydrocaulus. — The stems bearing the hydranths are 

 given off irregularly from the hydrorhiza, and very frequently 

 they are unbranched. When branching occurs, it is irregular, 

 as in text-fig, 1, ^-1. Groups of irregular anniilations are present 

 at the base of the stems, and at the points of origin of the 



