15 124 Proceedings of the Royal Irish Academy. 



proved to be Acrothrix mirabilis. The plants are indistinguishable in the 

 field, but with microscope the greater length of the peripheral filaments of 

 the present plant are at once noticeable. Found floating near Achill Bridge 

 and at Old Head, September, 1911. 



Acrothrix mirabilis Kylin ('07, p. 93). 



The specimens on microscopic examination were at first determined as 

 Mesogloia neglecta Batters, with which they agree closely ; butDr. Kuckuck 

 informs me that they are identical with A. mirabilis Kylin, authentic 

 material of which he has seen. Kylin's genus is based on a good character, 

 and should be maintained ; but if the two plants are synonymous, Batters' 

 specific name should be employed, as he first detected and published the 

 species (Journ. Bot., 1906, p. 2). A difficulty, however, presents itself, since 

 the type of M. neglecta cannot be found in the Batters collection, and hence it 

 is impossible to re-examine the points in which the Clew Bay material differs 

 from the description. The discrepancies are trivial, but until we are certain 

 that all the Mesogloiae of our shores are known, it seems wiser to let M. neglecta 

 stand as a separate species, and not to link it with A. mirabilis. 



The present plant bears a striking resemblance to M. Grijfithdana, and 

 was assumed to be such on collecting. It is remarkable also that it was found 

 in practically the same localities. Four plants in all were taken, two at Old 

 Head and two at Achill Sound, July, 1910. 



Leathesia crispa Harv. 



A few specimens of L. crispa were collected during the first trip to Clare 

 Island, but on no subsequent visit. In Journ. Bot., xlvi, p. 329, I have 

 dealt with the synonymy and distribution of this species. 



Fucus ceranoides L. 



Invariably present where fresh-water streams occur on sheltered shores. 

 (See pp. 83-88.) 



F. spiralis L. 



For remarks on the various forms assumed by this species see Fucaceae 

 associations (pp. 23 and 51). One variety, however, requires special notice. 



Var. nanus Stackh. — In many spots in Achill Sound, the sheltered form 

 of var. nanus is found growing on vertical peat-banks at high-water mark. 

 An unbroken series may at times be traced from the normal form. The 

 plants measure 1-4 inches in length, are slightly (1-3 times) branched, and 

 fruit freely at the proper season. In many of the receptacles examined 

 the oogonia were unripe (May) ; but they appeared to be perfectly healthy 



