1898-1902. No. 33.] UPPER DEVONIAN FISH REMAINS. 53 



remains of the large Bothriolepis and one toolh of a rhizodont fish, 

 which I have been unable to determine more exactly. I therefore assume 

 that we are here concerned with pure lacustrine formations. The sea 

 must therefore be assumed to have retired still farther. 



Conditions of Age. 



As previously emphasised, (p. 16) I assume in contrast to 0. E. MEYER, 

 that the uppermost part of the marine series D is not High Upper 

 Devonian (Chemung), but must be accepted as belonging to the lower 

 part of the Upper Devonian, or preferably as a transition stratum from 

 Middle Devonian to Upper Devonian. This view is confirmed by the 

 fauna of Series E. 



In the middle of this series we find the abundant fish horizon of 

 Skrap Valley. Amongst the forms found there, special interest must be 

 attached in this connection to the tiny mussle Phtonia, which appears 

 in such large quantities, and which seems to be identical with or at 

 least closely related to Ph. cylindrica HALL from the Hamilton group 

 in New York. Amongst the fishes certain forms such as Holoptychius 

 and Bothriolepis, according to our present knowledge, do not give any 

 more definite information than that we are concerned with Upper Devonian 

 strata. Others on the contrary, distinctly indicate that this horizon does 

 not belong to the upper part of the Upper Devonian. Thus Psammosteus 

 appears in Russia in the Middle Devonian (Poland) and in the lower part 

 of the Upper Devonian (Baltic Provinces). In Scotland a fragment was 

 discovered in the Middle Devonian (Caithness flagstones of Wick). The 

 third region in which this family is known is Spitzbergen; it was there 

 found in the fish horizon at Mimers Valley of presumably Upper Devonian 

 strata, but of no definitely determined age. The Glyptolepis scales entirely 

 agree with the European species, (leptopterus Ac. and paucidens AG.) 

 which are typical of the Scotch Middle Devonian series of Old Red 

 (Orkadian). In the Baltic Provinces the genus is found sometimes in 

 the lower sandstone of Middle Devonian age, and at other times in the 

 upper sandstone which must be regarded as Low Upper Devonian. In 

 Canada, a kindred form occurs in the fauna of Scaumenac Bay, which 

 must be considered to be Upper Devonian, although no closer determina- 

 ton is possible. FRECH 1 places it with the older Upper Devonian. 



Lethaea palaeosoica, Vol. II, pg. 232. 



