264 Geological Society. 
These, with the Domerian, each contain on an average about 
ten hemere, the grouping being controlled by the dominance of 
ammonite families or phases thereof—thus, Domerian: Age of 
Amaltheids; Raasayan: Age of Deroceratide and Hchioceratide. 
It is obvious that, with this increase in the number of hemere, 
the number of local non-sequences is greatly increased. Some 
comparative diagrams illustrate this. 
One of the most interesting discoveries which has resulted, partly 
from the great thickness of Scottish strata investigated and col- 
lected from, partly from comparisons with other areas, is that the 
so-called ‘armatum Zone’ of the English Midlands and that of 
the Radstock district, of Yorkshire and of the Scottish Isles, are 
not isochronous, but are separated by a time-interval which cor- 
responds to a thickness of some 300 feet of deposit in the Scottish 
area. ‘Thus, instead of the simple descending sequence 
Deroceras armatum 
Echioceras raricostatum, 
there is this sequence ascertained : 
An upper Deroceras horizon, 
An upper Echioceras horizon in three distinct stages, 
A lower Deroceras horizon, 
A lower Echioceras horizon with some Armatoids ; 
and even now possibly this is not the end of the complication, 
This alternation of Deroceras and Echioceras involves a pheno- 
menon which the Author calls ‘faunal repetition,’ and it is a 
reasonable supposition that this is not a solitary case—that is to 
say, doubt is at once thrown on the contemporaneity of other so- 
called ‘zones’ where they have been determined in different areas by 
the presence of certain species of a genus—the species admittedly 
not the same—or by the alleged presence of a single species on 
specific determination insufficiently rigid. The cases of zones 
determined on the dueus a non lucendo principle—the strata in 
correct intermediate position, but with the index zonal species 
conspicuously absent—seem especially to invite scepticism. 
. Three appendices are given—one, paleontological, containing 
descriptions of certain notable species, mostly new; another, his- 
torical, containing notes on certain ammonites described and figured 
by Wright in a paper published some years prior to the issue of 
his Monograph: it affords clues to the interpretation of his 
species, to the recognition of some of his missing types, to the 
identity of certain figures in Reynés’s Monograph, and to the geo- 
graphical distribution of species—a matter of particular importance 
in regard to faunal dissimilarity ; the third, geological,—a com- 
munication by Mr. J. W. Tutcher, embodying his reading of the 
sequence in the lower part of the Lower Lias carried down to the 
base of the Hettangian. 
P aad 
