20 INVERTEBEATE ANIMALS. 



Group 56.— Family PECTENID^ and allies, pecten, a 

 comb. Estimated number of species : recent, 220 ; 

 British, 13 ; fossil, 600. Carboniferous, &c. 



H Examples of Pecten, Lima, Eadula, Hinnites. 



P. Proteus, exhibiting contrasts of colour between 

 specimens of the same species. Lima excavata, 

 North Sea. R. M'Andrew. 



Group 57. — Family ARCID^ and allies, area, a chest. 

 Estimated number of species : recent, 341; British, 11 ; 

 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. 



^ Examples of Area, Trigonia, Nucula, Yoldia, 

 Leda, Gucullcea, Pectunculus, Adrana. 



Group 58. — Family AVICULID^ and allies, diminutive 

 of avi?i, a bird. Estimated number of species : recent, 

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



U Examples of Pinna, Meleagrina, Avicula, Perna, 

 Crenatula. 



Upper Compartment, 



Large group of Vulsella in sponge. 



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

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

 fossil, 220. Silurian, &c. 



IT Examples oiMtlieria, Mulleria, Mytilus, Crenella. 

 Myrina. 



Upper Compartment. 

 Lithophaga in stone. 



