MOLLUSCA (EXCEPT CEPHALOPODA). 
143 
from J>ritish localities of con-esponding age; the large 
riciirotomaria Frofeus aud tlie great limpet Patella Tessoni 
cannot fail to attract attention. The shells on the middle 
slope range from Calloviau to Corallian, and among the 
lamellibranchs Diceras with its two curly horns should 
particularly be noticed. Shells from the Solenhofen litho- 
graphic stone and other rocks of Kimmeridgian age, with 
many from the Portlandian, occupy the top slope ; most are 
from French localities. 
The Cretaceous series from Neocomian to Cenomanian 
comprises specimens from all quarters of the globe. The 
most remarkable are the Diceratidae and their descendants. 
Diceras and Toucasia, already noticed, are fixed to the sea- 
floor by one valve, just as is tlieii- more ordinary relation 
Chavia. In them, however, this fixed valve becomes very 
long, and is often twisted, w'hile the other valve is smaller 
and may be reduced to a .simple lid, as in Fequienia. In 
MonopUiira and Caprotina it will be seen that the fixed 
valve is less twisted, and that it grows upwards like a 
cup-coral. Like a coral, too, its lower part is often cut off 
by partitions. The likeness to a coral is still greater in 
Hippurites, of which a simple form is on the bottom slope, 
and more complicated forms on the top slope. Here too is 
Fadiolitcs, with a massive shell-wall broken up into cubical 
cavities. Meanwhile the other valve has become a stout lid 
with gi-eat projections inside, presumably for the attachment 
of muscles. The Rudistae, as these later types are called, 
reach their acme in Turonian and Senonian times with 
marvellous forms whose true nature must for ever have 
remained a mystery had we not been able to trace their 
gradual evolution. In Southern Europe and in the East 
and West Indies (e.g. Barrettia) they formed reef-like masses, 
now known as Hippnrite Limestone. The remainder of the 
Upper Cretaceous Mollusca are in Case 5a, and adjoining 
are specimens of Inoccramus expansus from S. Africa. 
Tertiary. The very complete series from the Paris 
Basin has an added interest Irom the fact that most of 
the specimens were purchased from the eminent fossil 
conchologist, G. P. Deshayes. The Eocene shells are closely 
allied to those found in England, but are better preserved, 
and the species are more numerous. The map showing the 
formations and localities is taken from “The Eocene and 
Oligocene Beds of the Paris Basin,” by G. F. Harris and 
H. W. Burrows (London, 1891), a work that gives also a 
Gallery 
VIII. 
Wall-ease 
6 . 
Wall-case 
5b. 
Wall-case 
5a. 
Between 
Wall-cases 
4 & 5. 
Wall-cases 
4-1. 
Between 
Wall-cases 
3 & 4. 
