177 



45. Ilimantidium undulatum, Ralfs. 



46. „ bidens, W. Sm. 



47. Tabellaria fenestrata, Eiitx. 



48. ,, ventricosa, Kiiu. 



49. Epithemia turgida. 



50. „ gibba. 



51. Eunotia gracilis. 



52. , tetraodon. 



53. Eunotia Diadema. 



54. Synedra capitata. 



55. „ biceps. 



56. Fragillaria....capucina, Kiitz. 



57. Ortboseira orichalcea, Jr. .Sm. 



58. „ nivalis, W. Sm. 



59. Nitzschia sigmoidea, W. Sm. 



Tho 60th is the unknown or doubtful species, which is from ^^-^ 

 to ilij of au inch long, and has 44 cross striae in iq\q of an inch. 

 In has generally the form nearly of a narrow plano-convex lens, with 

 two notches near the ends of the plane side. It seems to approach 

 Eunotia arcus (Kutzing\ but requires further investigation. In the 

 mean time, Mr Smith proposes to call it Eunotia incisa. 



The Mull earth is characterised by the great abundance of Pin- 

 nularise, Naviculee, and Stauroneides ; by that of Gomphonema co- 

 ronatum, of the Cymbellse, of the Himantidia, Eunotise, and Epi- 

 themiee, of Tabellarise, and of Eunotia incisa. 

 Its chemical analysis yielded 



Silica, 70-75 



Protoxide of iron, with traces of manganese, and 



an appreciable amount of phosphoric acid, 15*04 



Organic matter, . . . , . 12*36 



Water and loss, ..... 1-85 



100-00 



Its composition renders it probable that it may be useful as a ma- 

 nure. It may also be made to yield an excellent polishing powder. 



This earth occurs in a hollow, formerly a small loch in winter 

 and a pool in summer, now drained, lying in a rough piece of ground, 

 a mile or a mile-and-a-half in extent, between Loch Baa and the sea, 

 and about 30 or 40 feet above the sea-level. It rests on gravel, and 

 the gravel rests immediately on the granite of the district. It is im- 

 possible to fix precisely the age of the deposit, but, from the species 

 it contains, it is probable that it is not of very recent origin ; while 

 yet its epoch must be supposed subsequent to that of the deposition 

 of the gravel in which it is found. 



Specimens of the earth, and drawings of a number of the species 

 were exhibited ; also specimens of polishing powder made from the 

 earth. 



