432 RET. J. M. CEOMBIE ON LICHENS 



exception perhaps of Verrucarias, very little was overlooked. 

 Taking into account the small size of the island, which is only 

 about 11 miles long by 5 miles broad, the fact that no portion of 

 it is more than 1100 feet above the sea-level, or more than three 

 miles from the sea-shore, and the nature of the rock, which is en- 

 tirely volcanic, consisting of alternating layers of basalt, laterite, 

 and in the upper parts trachyte, with portions of upraised coral 

 reef chiefly on the S.W., and more especially the circumstance 

 that the island is very dry, more so no vv than formerly, when the 

 vegetation was more abundant, we should not infer that its lichen- 

 flora would be very extensive. Accordingly Dr. Balfour's collec- 

 tion of some eighty species and varieties, of which nearly one 

 half are new to science, may certainly be considered to consti- 

 tute as large a list as could reasonably be expected to occur. 

 Indeed it contrasts very favourably in this respect with the 

 recorded lichen-flora of the neighbouring islands of Mauritius 

 and Bourbon, which are not only of much larger extent, but also 

 in all other respects more favourably circumstanced for the growth 

 of lichens. This will appear when we mention that the lichens of 

 the Mauritius, as enumerated by Dr. Weddell, in vol. vii. (n. ser.) 

 of < Trans. E. Soc. Arts & 8c of Maurit,' 1873, amount to eighty- 

 nine species and varieties, whilst the list of Bourbon lichens given 

 by Nylander in ' Ann. des Sci. Nat.' ser. 4, t. xi. 1859, consists of 

 125 species and varieties. ■ — 



In the determination of the Bodriguez novelties, I have again 

 to acknowledge the valuable assistance of Dr. William Nylander, 

 F.M.L.S., who has also kindly sent me his MS. diagnoses of the 

 species determined by him. 



Family COLLEMACEI. 



I 



Tribe Collemei. 



COLLEMA, sp. ? 



Several specimens of a Collema occur which externally bears 



some 



flaccidurn 



and with the thallus discoloured so as to be quite indeter- 

 minable. 



On trunks of trees. Coll. Balf. no. 2202. 



