476 



Linncean Society . 



Mr. William dimming presented specimens of Layurus ovatus, 

 Briza maxima, and Mentha crispa, gathered by him in the vicinity of 

 Saffron Walden, Essex. 



Read, " On a White Incrustation on Stones, from the bed of the 

 river Annan." By Edwin Lankester, M.D., F.L.S. 



During a short stay which the author made last summer on the 

 banks of the Annan, in Dumfries-shire, his attention was arrested by 

 the appearance of the stones on the banks of the river. Wherever 

 a mass of gravel was exposed to the air, the surface of the stones 

 appeared covered with a white incrustation, as if they had been 

 white-washed. This appearance was more or less general on all 

 the exposed banks, but was most evident on the stones nearest the 

 water's edge. On examining the stones with a pocket- lens, their 

 surface appeared covered with acicular crystals, and from this it 

 was at first concluded that the incrustation arose from the crystalliza- 

 tion of some salt abounding in the waters. On procuring, however, 

 some stones from the water itself, they presented on their surfaces 

 the filaments of a minute conferva, which appeared to be the source 

 of the white crust ; but as the existence of the conferva would not 

 explain the crystalline appearance, it was examined under the micro- 

 scope, and the appearance was found to proceed from minute acicu- 

 lar bodies about yJo tn °^ an ^ ncn l° n & ana " 2 oV o tn °f an mcn Droa d, 

 which were most of them arranged in a stellate form, but many 

 were scattered in all directions. Running under the whole were 

 the filaments of a minute conferva, on which the acicular bodies 

 rested. 



In Greville's Scottish Cryptogamic Flora, these bodies are referred 

 to the genus Exilaria, but the stellate arrangement of the aciculse 

 gave them a different character to E. fasciculata. Hooker, in his 

 continuation of Smith's ' English Flora,' has placed Greville's supposed 

 plant as a synonym of Diatoma truncatum, from which D. fascicular 

 turn is not distinct. 



In Ehrenberg's great work on the Infusoria, these bodies are 

 figured and described under the head of Polygastric animalcules 

 (p. 11. tab. xvii.) of the family Baccillaria. The genus to which 

 they belong is Synedra, and is distinguished by the animal being 

 furnished " with a simple siliceous prismatic carapace, when young 

 attached by one end, when old often free, without any or only a 

 slightly marked pedicel." The species which it most closely re- 

 sembles is the Synedra Ulna (common Eel -animalcule), which is 

 characterized by being striated with linear corpuscles, straight, trun- 

 cated at the sides, flat on the back and belly, with the apex a little 

 dilated as they become aged. The bodies from the Annan are not 

 striated, nor are their ends dilated, although they appear full-grown. 

 The siliceous skeletons in which these little animals are invested, 

 will account for their white appearance. Although these bodies 

 have been often described both as plants and animals, no notice 

 appears to have been given of their producing the phenomenon 

 here described. 



