408 THE OCEAN WORLD. 



has there been such a wholesale extinction of species. The great 

 family of Spiriferidae is wholly extinct, and of 400 species belonging 

 to the family of the Rhynconellidce only four are now living. Species 

 of the curious genera Crania, Discina, and Lingula are still living, 

 and are mostly found in the seas of the southern hemisphere. 



The Brachiopoda contain the following families : — 

 I. Lingnlidcs, containing Lingula and other genera. 

 II. Disdnidce, containing Sipbonotreta and Discina. 



III. Craiiiadiv, containing Crania. 



IV, Froductidce, containing Chonetes and Productus. 



V. Orthidce, containing Calceola, Davidsonia, Strophomena, and 



Orthis. 

 VI. Rhyjiconellidce, containing Atr)'pa, Pentamerus, and Rhyn- 



conella. 

 VII. SpirifcndcB, containing Uncites, Retzia, Athyris, and Spiri- 

 fera. 

 VIII. TerehratulidcE, containing Thecidium, Argiope, Terebratella, 

 and Terebratula. 



