DESMID FLORA OF A TRIASSIC DISTRICT. 145 



than in otiier parts of the bog, and that the Desmid flora has 

 been expelled by the more vigorous competition of the Diatom 

 growth. This bog, with a census total of 138, must be considered 

 rich, having regard to its small dimensions. Like the Harcombe 

 bog it produces no member of the genus Mesotaenium, nor 

 does it appear to contain any member of the genus Arthrodesmus, 

 and only Xanthidium armatum in the genus Xanthidium. 



Ring i' th' Mire Bog. — Considerable interest attaches to 

 this station on account of its position and the beds upon which 

 it is situated. It is at the highest altitude in the district, 812 

 feet, on that portion of the East Devon plateau known as Broad 

 Down. This is an extent of stifi Cretaceous clay intermixed 

 with flint and chert. Here and there are shallow depressions 

 of no extent which become filled during the winter rains and 

 gradually dry up as summer progresses, unless a wet season 

 keeps refilling them. The small bog known as " Ring i' th' Mire " 

 is the only approach to a permanent bog on the plateau, and it 

 almost dries out in a dry summer. Although local legends 

 have no value as scientific evidence, there may always be a 

 residuum of truth in them, and a local legend connected with 

 this spot indicates a much more extensive " mire " in former 

 times, so that the Desmid flora at present existing may be re- 

 garded as the remnant of a much more extensive one. The bog 

 is so situated that no contributions to its Desmid flora could 

 possibly be made from stations of superior altitude. It is quite 

 isolated, and must have been so since Gittisham Hill, upon 

 which it stands, was severed from St. Gyres Hill across the valley 

 of the Otter. The Desmid flora of this bog may therefore be 

 regarded as the survival of an ancient Desmid flora derived 

 from the Blackdown Hills when the land surface between was 

 of more or less uniform level. It will be seen that, situated as 

 it is upon Cretaceous beds, it has strictly speaking no place in 

 this paper, and is included merely for comparison with other 

 stations in the district, and because of its unique position. The 

 total census number, 118, is sufficiently striking, having regard 

 to its extremely meagre proportions and to the fact that during 

 the greater portion of the vegetative season it is almost com- 

 pletely dry. 



Pools and Ditches. — Small pools such as occur plentifully 

 in more level counties are very infrequent in East Devon on account 



