ALCYOXIDIUM PARASITICUM. 503 



Habitat. On the stems and branches of Sertularian Hy- 

 droids (especially Hydrallmania falcata), which it invests 

 with an earthy coating. 



Localities. St. Andrews, abundant (Reid & Mcintosh) : 

 Northumberland, common (Alder) : Filey ; Menai Straits ; 

 South Devon, not common (T. H.) : Cornwall (Couch) : 

 Ireland, north and east shores (W. T.) : Dublin Bay, 

 common (Hassall). 



Geographical Distribution. Bahusia, not rare (Loven) . 



Descriptions of this species have commonly been founded 

 on dried specimens, and have therefore failed to represent 

 its true character. In this condition it appears as an 

 earthy incrustation, with a porous surface (Plate LXIX. 

 fig. 5). Smitt has given us an account of it, founded on 

 Loven^s detailed observations, which leaves little to be 

 desired"^. 



The younger marginal cells are somewhat elongate in 

 shape, with distinct septa and a finely granulated surface. 

 In the older portions of the colony they are shorter, with 

 a circle of minute papillae, a little within the margin, 

 forming an opaque border, in the midst of which there is 

 a rounded area, covered by a hyaline membrane. In the 

 oldest cells the septa are no longer visible, the papillae are 

 irregularly placed, or form several rows round the central 

 area, which still retains the transparent membranous cover- 

 ing. In all cases the zooecia are exceedingly small. 



* It should be noted that Hassall's brief description of this species (the 

 true nature of which he seems to have been the first to determine), published 

 in 1841, agrees substantially with Loven's. 



