286 Proceedings of the Royal Physical Society. 
occurrence in other parts of the county I have never 
been able satisfactorily to convince myself! But these are 
exactly species which are abundant both in Orkney and in 
the Moray Firth nodules, so that, strange to say, the 
Achanarras list reads more like one from either of these 
regions than from Caithness, at least as hitherto known. 
As the fishes which are peculiar to this quarry, so far 
as Caithness is concerned, are not found even at the localities 
for fossils which are nearest to Achanarras, namely Spital, 
Banniskirk, Westerdale, and Achalibster, it follows that 
peculiar interest must attach to the exact stratigraphical 
position of the beds in which they do occur. This is a 
problem which it is, however, best to leave in the hands of 
the officers of the Geological Survey. 
XXI. River Temperature. Part I. Sts Daily Changes and 
Method of Observation. By H. B. Guppy, M.B. 
[Plate VIII.] 
(Read 17th January 1894. ) 
When some time ago I accepted the invitation of the 
Secretary to prepare a paper for the Society on the tempera- 
ture of rivers, I set busily to work with his assistance to 
supplement my own observations on the Thames with those 
of observers on other rivers. The result was, that in time 
my note-books were filled with ideas and facts; but, as the 
inquiry proceeded, the ideas disappeared and the facts alone 
remained, and I found myself face to face with a problem 
that demands, even for a preliminary investigation, a vast 
amount of labour, and for its ultimate solution, a very much 
more uniform line of research. Uniformity of method is 
sadly lacking in the work of all observers, my own included, 
and one of the first requisites is, by a careful study of the 
daily thermal regime of a river, to bring all these data into 
1 This, as regards Diplopterus, will appear a strange statement to many 
- who are familiar with Hugh Miller’s writings, but there can be little doubt 
that the Thurso ‘‘ Diplopterus,” whose cranial buckler is figured in the 
‘‘Footprints,” is Thursius pholidotus. Thursius macrolepidotus, too, has 
often done duty for ‘‘ Diplopterus,” as well as for ‘‘ Osteolepis” macrolepidotus. 
