INVERTEBRATE ANIMALS. 21 



fossil, 600. Lower Silurian, &c. Trigonia, justly 

 admired for the beauty of its pearly interior, and now 

 found only in Australian Seas, is represented by many 

 species in the Mesozoic rocks of Britain. 



H Examples of Area, Trigonia, Niicula, Yoldia, 

 Leda, Cucullcsa, Pectimculus, Adrana. 



Group 58. — Family AVICULID^ and allies, diminutive 

 of avis, a bird. Estimated number of species : recent, 

 100 ; British, 2 ; fossil, 450. Silurian, &c. 



IT Examples of Pinna, Meleagr'ina, Avicida, Penia, 

 Crenctula. 



Upper Compartment. 



Large group of Vidsella in sponge. 



Group 59.— Family MYTILID^ and allies. Mussels. 

 Estimated number of species : recent, 250 ; British, 12 ; 

 fossil, 220. Silurian, &c. 



^ Examples of Mtheria, Mulleria, Mytilus, Crenclla, 

 Myrina. 



Upper Compartment. 

 Lithophaga in stone. 



Group 60.— Family UNIONIDiE. tmio, a pearl. River- 

 mussels. Estimated number of species : recent, 574 ; 

 British, 4 ; fossil, 100. Tertiary. 



iy Examples of Unio, Anodonta, Mycetopus. 



Upper Compartment. 



British Pearls ; figures of Bhudda and artificial 



pearls in Unio plicatus. 

 Unio midtiplicatiis ; extensive fracture repaired in a 



very peculiar manner by the animal ; from the 



Gaskoin cabinet. 



