Browne: The Aquatic Coleoptera of the Isle of Man. 163 
running between the Isle of Man and Cumberland, and meeting 
the south tide in a line between Morecambe Bay and Maughold 
Head. 
Thus the main bulk of the flora of the land and fresh-water 
mollusca, and of the water beetles, and probably of the other 
groups, has reached the Isle of Man in spite of adverse winds 
and currents, and this fact is at least suggestive that they 
covered the intervening region by spreading along a land- 
bridge which has since completely disappeared. 
With. regard to the southern element in the fauna and flora 
Dr. Scharff apparantly thinks that it was present in the north 
of England even during the ice-age, in which case of*course it 
would have travelled with the main fauna and flora to the Isle 
of Man. On the other hand there seem to be strong objections 
to Dr. Scharff’s views on the distribution of the fauna and 
flora in England and Scotland during the glacial period, and 
it is, perhaps, reasonable to entertain the possibility of the 
species of this group having taken advantage of wind and 
tide, and having reached the island from the south and west. 
Considering the extraordinary multiplicity of contrivances 
for dispersal possessed by so many animals and plants it seems 
to me unsafe to assume land-bridges to account for insular 
faunas and floras unless definite geological evidence is forth- 
coming, or unless the biological facts point to this method as 
the only possible explanation. 
BIBLIOGRAPHY. 
1855. CLaRK. ReEv.- HAMLET. ‘Synonymic List of the 
British Carnivorous Water Beetles, together with 
Critical Remarks and Notices of Foreign Allied 
Species.’ ‘ Zoologist,’ pp. 4859-60. (A black 
var. of Deronectes 12-pustulatus ‘in a small stream in 
Isle of Man’). 
1862. STOWELL, Rev. HucH A. ‘ Notes on the Entomology 
of the Isle of Man.’ ‘ Entomologist,’ xx, pp. 7895- 
7918. 
1887. FowLer, Rev. W. W. ‘Coleoptera of the British 
Island,’ Vol. I., p. 191. (Mentions Agabus bigutiatus 
from Isle of Man). 
1904. Tomitn, B. ‘Some Notes on Manx Coleoptera.’ 
“EIMiuM:; Ser:°2;'xv) pp. §77-£79: 
1905. Tomitn, B. ‘Further Notes on Manx Coleoptera.’ 
Ibid., xvi, pp. 252-4. 
1908. BarLey, Dr. J.H. ‘ The Coleoptera of the Isle of Man.’ 
Vice-Presid. Address: 31st Ann. Rep. and Proc. 
Lancs. and Cheshire Ent. Soc. for Session 1907, pp. 
18-40, 
igit April.1. 
