plants, placed side by side on the table of the microscope, has 

 convinced me of their perfect distinctness. In E. distortus the 

 endochrome is small, leaving wide dissepiments and colourless 

 borders ; the substance is exceedingly tender, and the branches 

 break up into innumerable frustules when re-moistened. In fact, 

 it is impossible to trace the ramification from the extreme rotten- 

 ness of the moistened frond. In E. Landsburgii on the con- 

 trary, the endochrome completely fills the cavity ; the dissepi- 

 ments are mere lines ; and the substance is exceedingly tough, 

 and may be kept in fresh water for hours or days, without 

 injury. These characters appear to me sufficient. We must 

 also bear in mind that E. distortus is a littoral species, while our 

 new species has only been found by dredging in deep water. It 

 appears to be of rare occurrence. Mr. Landsborough found 

 only a few small tufts ; nor was I much more fortunate in col- 

 lecting it at Roundstone. It is satisfactory to know, however, 

 as establishing the character of the species, that the specimens 

 from the west of Ireland agree in all respects with those from 

 Scotland. 



Fig. 1. Ectocarpus Landsburgii: — of the natural size. 2. A branching 

 portion. 3. Part of the same. 4. Transverse section of the stem : — all 

 more or less highly magnified. 



