MOLLUSCA (EXCEPT CEPHALOPODA). 



143 



PleuTotomaria Froteus and the great limpet Patella Tessoni 

 cannot fail to attract attention. The shells on the middle 

 slope range from Callovian to Corallian, and among the 

 laniellibranchs Liceras 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 Cenoinanian 

 comprises specimens from all quarters of the globe. The 

 most remarkable are the Dicer atidae and their descendants. 

 Diceras and Toucasia, already noticed, are fixed to the sea- 

 floor by one valve, just as is their more ordinary relation 

 Chama. In them, however, this fixed valve becomes very 

 long, and is often twisted, while the other valve is smaller 

 and may be reduced to a simple lid, as in Requienia. In 

 Monopleura and Caprotina it will be seen that the fixed 

 valve is less twdsted, and that it growls upw^ards 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 

 Eadiolites, with a massive shell-w^all broken up into cubical 

 cavities. Meanwhile the other valve has become a stout lid 

 with great 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 Hippurite Limestone. The remainder of the 

 Upper Cretaceous Mollusca are in Case 5a, and adjoining 

 are specimens of Inoceramus expansits from S. Africa. 



Tertiary. The very complete series from the Paris 

 Basin has an added interest from 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 " Tiie Eocene and 

 Oligocene Beds of the Paris Basin," by G. E. Harris and 

 H. W. Burrows (London, 1891), a work that gives also a 

 full list of the Mollusca. Below it are fine sj)ecimens of the 



Gallery 

 VIII. 



Wall-case 

 6. 



Wall -case 

 5b. 



Wall-case 



5a. 

 Between 

 Wall-cases 

 4 & 5. 



Wall-cases 

 4-1. 



Between 

 Wall-cases 

 3&4. 



