96 6 Proceedings of the Royal Irish Academy. 



and again at Eoundstone in Galway Bay, on extensive sand-dunes. During 

 the progress of the Clare Island researches Eev. W. F. Johnson met with the 

 insect on sand-hills at Keel, which is also in Achill, and on the mainland at 

 Mulranny, and on sand-hills at the southern entrance of Achill Sound ; and, 

 as stated above, Mr. Stelfox took it on sand-hills near Belmullet. In the 

 British Islands, therefore, the insect has hitherto been taken exclusively on 

 sand-hills. In Ireland the length of the coast-line from Ballycastle to Eound- 

 stone, without comiting indentations and narrow-mouthed bays, may be stated 

 roundly as 230 to 250 miles. If we are to postulate that this puny insect crept 

 along the shore, and was obliged to follow all the indentations of this extremely 

 broken coast-line, much of it rock and precipice, as well as the banks of 

 rivers which debouch into the sea, the suggestion is plainly an impossible 

 one. Its isolated stations along the shore might be reached if the female 

 could be transported by water. But a coast-wise dispersal thus on the 

 storm-tossed waves of the north and west of Ireland is unthinkable. 

 Geologists are now almost agreed that neither the ancient fauna nor flora of 

 Ireland could have survived the Ice Age. And we will not here discuss the 

 land-connexions of this island with Scotland and Scandinavia, nor with 

 England and the Continent. But if we predicate its arrival, perhaps via 

 England, at an early epoch, at a time when the Boulder-elay was being broken 

 down by frost and alternating temperatures, the scanty and eager herbage 

 which could grow on the stony and barren debris would be widespread, and 

 as in the course of ages the soil became more fertile in humus, a richer and 

 more aggressive flora woidd drive the weaker plants to the banks of streams, 

 the sides of hills, and the sea-shore, and with it the insects that were dependent 

 on them for nourishment. Hence isolated colonies would be found in such 

 localities, having radiated in all directions from central districts now become 

 unsuitable. But it may be said that of some twelve moths, which also have 

 apterous females, Ireland reckons nine as indigenous. Do not the same 

 problems present themselves in their case ? The reply is a simple one, and, 

 moreover, seems to indicate that they arrived overland before this country 

 was insulated. The nine others are tree-feeders, and the caterpillars, hung by 

 a silken web, are blown from tree to tree, and the females are active and 

 climb the trunks in winter. They therefore accompanied the bushes and 

 trees on arrival: Moreover, with the exception of one which is polyphagous, 

 all are in flight as imagines in the winter or early months of the year. The 

 females, being apterous, are therefore not blown away from their food-plant, 

 as would be the case with such weak fliers as are the males. Perhaps Nyssia 

 has reaped a similar advantage on the wind-swept heights and shores it 

 inhabits. But to return to the list : — 



Larentia salicata, which is usually a local species, occurs on Clare Island 



