No 3 ] REMARKS ON NORTHERN LITHOTHAMNIA. 129 



As I observed above, L. macrocarpum and L. hapalidioides 

 are hardly distinguishable one from the other. Certainly they are, 

 as a general rule, growing on heterogeneous substrata, the former 

 occurring on other algae of frequently rather loose consistency, 

 whereas L. hapalidioides appears on different shells of molluscs. 

 I have, however, under L. macrocarpum instanced the occurrence 

 of this species on shells of mussels appearing among such algae 

 on which the species is generally growing. Besides I have stated 

 that it is likely to appear also on other calcareous algae which 

 occur in similar condition of things, which, by the bye, seems to 

 be the case with both species. On the other hand L. hapalidioides 

 seems likely to occur on algae of rather loose consistency in the 

 same conditions of things in which L. macrocarpum appears on 

 substratum of hard consistency. This is e. g. the case with a 

 specimen of Melobesia confinis in Crouan's herbarium which 

 partly sticks to Oelidium corneum. As I have remarked 1. c. it 

 spreads to Oelidium probably from the shells of Balanides, which 

 it also partly covers, the shells forming a part of the substratum 

 of the said species. Some specimens, distributed by Le Jo lis 

 under the same name, growing on Oelidium, are partly encom- 

 passing the branches of the host plant, partly forming crusts over 

 small shells of Balanides and other objects as well as over and 

 between the branches of Oelidium. I am, however, not sure 

 whether the latter form should be referred to L. hapalidioides. 

 Although it is thus almost impossible to draw any line, I do not 

 venture at present to subsume this species under L. macrocarpum, 

 but admit it for the present as independent. On the other hand 

 this species approaches Lithoph. (Dermatolithon) prototypum Fosl. 

 from the West Indies. 



The form confinis I take here in a somewhat altered sense. 

 In the sense taken by Orouan it embraces partly L. macrocar- 

 pum, partly typical L. hapalidioides, whereas the specimen men- 

 tioned above, partly growing on Oelidium, is a little diverging 

 from the typical form of the latter species and in part almost im- 

 bricate. I circumscribe the form to only embracing specimens with 

 fronds loosely and irregularly subsquamellate imbricate. In the 



