ADDENDA. 



(Including recently described species and changes in 



nomenclature.) 



The late Dr. Liitkemiiller, during the twenty years pre- 

 ceding his death, made some careful investigations of cell-wall 

 structure in Desmids, and as a result of his work a number of 

 species must now be placed in a different generic position from 

 that originally assigned to them. Several genera are concerned in 

 these changes, and the majority of the alterations in nomenclature 

 set down below are due to the researches of Dr. Liitkemiiller. 



Genus ROYA W. & G. S. W. (vol. i, p. 106). 



This genus was placed by its discoverers amongst the Placo- 

 dermse near to Closterium. It was represented as resembling 

 the latter genus very closely, the chief distinction between the 

 two genera being the occurrence of apical vacuoles in Closterium 

 and their absence in Roya, and furthermore, Closterium has usually 

 two chloroplasts with the nucleus in a median position, whereas 

 Roy a has a single chloroplast with the nucleus in a lateral notch. 

 More recent research has shown that whilst these supposed 

 distinctions do not invariably hold, the two genera are never- 

 theless less closely related than was at first supposed. 



The late Dr. Liitkemuller has pointed out (' Desm. Bohm.' 

 1910) that Roya has a very simple type of cell-wall structure and 

 cannot be allowed to remain amongst the Placoderm Desmids. 

 Its wall is destitute of pores and is a simple cellulose membrane, 

 and Dr. Liitkemuller has therefore suggested that it should be 

 placed among the Saccodermse near to Mesotcenium. The 

 position of Roya in vol. i, p. 106, next to Closterium is therefore 

 erroneous. 



With the discovery of the new species, Roya anglica West 

 (vide infra), the original description of the genus must of necessity 

 be emended, since this species possesses several characters not 

 included in the de-jcription given in vol. i, p. 106, e. g. the presence 



