28 Dansk Botanisk Arkiv, Bd. 2. Nr. 2. 



From Scytosiphon Rosenvingea differs especially in its rami- 

 fication and the want of paraphyses. 



With regard to the anatomical structure and as to the 

 arrangement and shape of the sporangia Rosenvingea comes also 

 near to Hydroclathrus and Colpomenia. 



Fa/77. 3. Mesogloiacece. 



Castagnea Derb, et Sol. 

 1. Castagnea Zosteræ (Mohr) Thur. 



Thuret in Le Jolis, Liste des Algues marines du Cherbourg, 1863, p. 85. 

 Farlow, W. G., The Marine Algae of New England, 1881, p. 86, pi. 7, fig. 2. 

 Bornet, E., Les Algues de P. K. A. Schousboe, 1892, p. 236. 



Rivularia Zosteræ Mohr, Bemerkungen über die Rothischen Rivularien 

 in Weber, Beiträge zur Naturkunde, vol. 2, 1810, p. 367. 



A great confusion as to the definition of species and also of 

 genera prevails in the group of Mesogloiaccæ, and several of the 

 species of earlier authors are sometimes referred to one form, 

 sometimes to another. When comparing my plant with earlier 

 described forms it seemed to me that judging from their figure 

 it showed no little likeness to Castagnea polycarpa Derb, et Sol. 

 But great similarity with Farlow's figure of Castagnea Zosteræ 

 was also obvious. On the other hand the method of growing in 

 my plant seemed to differ essentially from the description of 

 Schmitz (as to which more later) and having only very little 

 authentic material (and that only dried) to compare with I asked 

 Prof. Kuckuck as to his opionion of my plant. 



Prof. Kuckuck has now most kindly communicated to me 

 that it seems to him that my plant comes near to Castagnea 

 Zosteræ, but he added that he had not yet arrived to any definite 

 conclusion as to the generic and specific arrangement in the 

 group of Mesogloieæ. 



In the following I now give a description of my plant so 

 detailed that I hope it may be possible to recognize it when 

 Prof. Kuckuck's work: "Die Phæosporeen" has appeared. 



The specimens found were growing in tufts, 15 — 20 cms and 

 more high, epiphytic upon the leaves of Thalassia testudinum. 

 They were fixed to the leaves of the host plant by means of a 

 small disc. 



The central main filaments are connected rather firmly 

 together to form an axial fistulous layer, leaving a cavity open 



cryptostomata with numerous hairs around which the nearly cylindri- 

 cal plurilocular sporangia occur. 



