402 PROCEEDINGS OF THE ACADEMY OF [1896. 



ices are forms which would be apt to hide in minute crevices of bark 

 or holes in decaying timber. The Leptinaria lives on ferns, and its 

 minute size renders it possible that it might be carried on dead- 

 leaves, etc., which an exceptionally high wind blowing for eight or 

 ten hours might carry to the islands. Such winds are not unknown,, 

 especially in the tropics, and a single hurricane blowing in the 

 right direction might introduce a large number of seeds, insects, 

 fern spores and minute land shells, to say nothing of larger objects. 



It is obvious, therefore, that the derivation of the island flora and 

 land shell fauna does not present us with serious difficulties. Its 

 distinctively American type indicates the point of origin. Before 

 discussing this branch of the subject further, it may be well to refer 

 to the characteristics of the several islands, in order that the rela- 

 tions of the fauna to the fertile area may be considered. 



The islands which lie most directly in the track of currents and 

 winds are those of the southeastern group. Chatham is one of the 

 best known and most fully explored in the whole group, and is nota- 

 ble for the clean cut development of the three zones and the fertility 

 of its upper portion. On Charles there is less vegetation on the 

 lower levels but, according to Agassiz, the beach shows many planta 

 common to Panama and Guayaquil. Hood is so much lower than 

 the others (640 feet) as to be chiefly in the barren zone, covered 

 with lava blocks destitute of water in the dry season, and partially 

 green only in the rainy season. 



Of the Central group, Indefatigable is first in the track of the 

 current, and much resembles Charles and Chatham with a vast tract 

 of arable upland. Duncan is comparatively small with abrupt sides, 

 and has no living water, though its upper part is somewhat verdant. 

 The south and east parts of James Island seem partly sheltered by 

 Charles and Indefatigable from the prevailing trade winds ; at all 

 events they are dryer and less fertile than the portion north of 

 James Bay. Much of Albemarle Island is low and consequently 

 barren, having a desolate burnt aspect. The highlands of the 

 southern portion are covered with rich vegetation, and there are 

 elevated green patches near the northern end. Although there is 

 actually a larger area of vegetation on Albemarle than on either of 

 the other islands, yet the fertile region is not as large in proportion 

 to the total area as the size of the island on the chart would lead 

 one to expect. 



