754 Proceedings of the Royal Irish Academy. 



a series of forms belonging tlie same family but having the form of 

 cell-plates instead of filaments. 



These types have been little studied till lately ; in part owing to 

 the fact that they are almost entirely tropical in distribution, and in 

 part because many specimens being in a sterile state their affinities 

 could not be determined. 



During a short stay in New Zealand some years back, I collected the 

 two species which form the subject of the present Paper, and which 

 seem to me to constitute a not unimportant addition to our knowledge 

 of the group. Considering, however, that this group of plants is 

 so little known to English botanists ; that the literature is scattered 

 and the nomenclature already confused, I have thought it advisable to 

 give a short summary of previous observations before proceeding to 

 describe these species in detail. 



In 1870, Millardet^ (3), gave the name of Phycopeltis epiphyton 

 to small yellow discs, not more than 0*1 mm. in diameter, found on 

 leaves of Alies pectinata near Freiburg. They consisted of radial rows 

 of cells containing hamatochrome, as in Trentepohlia. Certain cells 

 of the disc not otherwise differentiated were observed to contain swarm- 

 spores ; but no pedicellate sporangia were found. Karsten (16), states 

 that the form is not uncommon near Allerheiligen, but he has also 

 been unable to find the second sporangium form. 



As far back as 1849, a very similar form had been observed by 

 Montague on reeds in Algeria. This is the Phyllactidium arundina- 

 ceum of Kutzing (4), but as the genus Phyllactidium has since been 

 absorbed in Coleochsete by Pringsheim (9) it will now be found under 

 Phycopeltis as Ph. arundinacea? It may perhaps be identical with 

 Millardet's plant, but neither of them show any characteristic fructifi- 

 cation, on which alone a species can be safely founded. 



The Chromopeltis of Eeinsch(5) found on leaves of mosses (Leskea) 

 in the Yosges in 1875, includes also discoid algse of the same kind but 

 similarly sterile. 



Mettenius (6) had observed similar algse on leaves of Hymenophyl- 

 lacese in South America, but in this case I believe no special name 

 was given. 



Bornet (7) also in 1873, described a yellow plate-like alga on leaves 

 in Brazil as forming the algal element of Opegrapha filicina. 



1 1 may add that I have myself looked for it frequently round Freiburg and in 

 the Black Forest generally, but without success. 

 2De Toni— Sylloge Algarum, I., 1889. 



