( 198 ) 



Professor Harvey has pointed out its close affinity with G. Turneri, 

 from which it differs in its rather shorter joints, more simple and erect 

 filaments, more obtiise at the apices ; the position of the tetraspores is 

 also different. In short, while some other very closely allied species 

 are allowed to retain their position, we hardly see how these two can be 

 united. 



Our present knowledge, however, of both species is very limited, and 

 we would earnestly invite the attention of observers to these minute 

 and obscure forms, in the hope that additional facts in their history may 

 be brought to light, and our knowledge of the species rendered more 

 accurate. 



CALLITHiMKION MESOCARPUM. 



EXPLANATION OP DISSECTIONS. 



Fig. 1. — Filaments with tetraspores. 



2. — Tetraspores from same. Both magnified. 

 Phj/c. Brit. 



