IGO (UTIDK To THK KOSSIL INVKHTKmUTK ANIMALS. 
Gallery 
VII. 
Table-case 
5. 
have descended from totally dilVereiit ancestors, and they may 
thus he placed in distinct genera, [)crhapsin distinct families. 
Unfortunately this method of study has not yet been i)ursned 
long enough for in\'estigators to have settled the numerous 
problems presentetl by the very large numbers of these 
fossils; nor are the solutions that have hitherto been pub- 
lished always found to agree. Hence the classification and 
nomenclature of the ammonites has for some years been in a 
state of tramsition, to the great perplexity of geologists who 
wish to use these widely-distributed fossils for the identifica- 
tion of various strata and to quote names long familiar in that 
connection but now requiring emendation. It is impossilde 
to alter the an’angement and naming of a great exhibited 
series like that of the British Museum to accord with a 
rapidly advancing classification. Tho.se important questions 
must be studied in original memoirs, and these pages can 
only mention a few of the more conspicuous specimens. 
The smaller ammonites in the Table-cases are arranged 
for the most part under the geological Ages, the foreign 
specimens of each Age being placed in the same Ca.se 
as the British ones. The larger specimens in the Wall- 
cases begin with Liassic forms in Cases 12 and 11, pass to 
l»ajocian in 10, and Oxfordian in 9; then, crossing the 
(lallery, continue with the uppermost Jurassic in Case G, 
Lower Cretaceous in 5, and Upper Cretaceous species in 
4 and 3. We begin with the oldest. 
From the Himalayan Trias are 
shown I't ijchit.es, Carnites, and Gym- 
nites, smooth shells, with sutures 
not far removed from those of 
goniatites. Among many specimens 
from the Upper Trias of Hallstadt 
in Austria, Monophyllites and Jiha- 
cophylUtcs, which have primitive 
sutures with leaf-like saddles, start 
the line of IMiylloceratidae. In 
rinacocems Mettcniichi, on the other 
hand, the sutures have already ac- 
quired an extraordinary complexity, 
as best shown in some large speci- 
mens and a section in AVall-case 12. 
Sutures of rather simpler type are 
clearly shown in specimens of Faracladiscites multilohatus. 
From St. Cassian in the Tyrol come the roughly-ridged shells 
Fia. 94 . — Ccratites nodosus 
from the Muschelkalk. 
