138 The Irish Naturalist. 



Probably we shall find that there are more fresh-water species. 

 It is due to Bornet and Flahault, that we have had pointed 

 out the great use of these plants in the economy of nature — 

 namely, that of shell-destruction. Since Bornet's work, 

 papers have been published, giving illustrated accounts of 

 two additional species, one by Batters^ and one by Bommer. 



The presence of these organisms can be detected in the 

 shells of various molluscs, such as razor -shells, limpets, 

 cockles, periwinkles, by the green, bluish green, or pink 

 stains which they make. They have been classified according 

 to their colour, into four groups : — 



I. Rhodophyceae (red); 2. Chloropli3^ceae (pure green) ; 3- 

 Cyanophjxeae or Phycochromacese (blue-green) ; 4. Fungi 

 (plants colourless, appearing to belong to the fungi). 



Care is needed in examining a specimen to make sure that 

 the plant we are looking at reall}^ penetrates into the shell, as 

 various algae, especially in the young state when the spores 

 are germinating, form patches of various colours on the 

 surface of shells, but never penetrate into their substance. 

 This mistake fortunatel}^ is easily avoided ; by using one or 

 other of the following simple tests we can determine whether 

 the coating is superficial or not. If we scrape the shell with 

 a sharp instrument (or, if this is not at hand, one'5 nail being 

 so, answers the purpose admirably) the young germinating non- 

 perforating seaweeds will be rubbed off, leaving the shell its 

 original colour. If the shell is penetrated by a shell- 

 borer this will not be the case, the colouration still being 

 apparent. Another and perhaps better plan is to break the 

 shell in two ; if the stain continues to any depth we ma}^ feel 

 sure that we have a perforating alga. A good deal of infor- 

 mation can also be obtained by powdering the shell with 

 pestle and mortar, and observing the powder under the i-inch 

 objective, or by taking a thin layer of the shell, and looking 

 at it under the same objective. 



For fuller information as to these plants it is necessary to 

 first remove the calcareous matter and thus set free the plants 

 themselves for examination. The reagent used is Perenyi's 

 Fluid, which not only dissolves the carbonate of lime, but 

 fixes the protoplasm, without destroying the colour. The 



^ Conchocelis rosea. E- Batters. Phycological Memoirs, II., 1893. 

 2 " Note sur Vcrru carta cotiseqiwis," 1892, C. Bommer, 



