THE TANGANYIKA PROBLEM. 297 



us with the first instance of an incrusting gymnoleamatous 

 fresh-water form. So far as I have been able to compare 

 it with the known marine forms of the gymnoleamata, this 

 new species from Tanganyika does not exhibit a close 

 identity with any of them. The colony in its general 

 character, and in some special features of the individuals of 

 which it is composed, is not at all unlike the marine genus 

 Arachnidium, and but for the greater irregularity of the 

 cells and the longer tubes which are associated together in 

 the Tanganyika species, I should have been inclined to 

 place it in that genus. Still, considering its remarkable 

 habitat, these structural distinctions, and also that I have 

 not yet had time to completely investigate the matter, I 

 think that the method least open to objection is to form a 

 new genus for its reception, and I therefore propose the 

 generic and specific names of Arachnoidia ray lankesteri, 

 leaving a fuller description of the organism for a separate 

 memoir. 



