408 
THE OCEAN WORLD. 
has there been such a wholesale extinction of species. The great 
family of Spiriferidze is wholly extinct, and of 400 species belonging 
to the family of the Rhynconellidee 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 :— 
VU. 
Lingulide, containing Lingula and other genera. 
. Discinide, containing Siphonotreta and Discina. 
. Craniade, containing Crania. 
Productide, containing Chonetes and Productus. 
Orthide, containing Calceola, Davidsonia, Strophomena, and 
Orthis. 
Rhyncondlide, containing Atrypa, Pentamerus, and Rhyn- 
conella. 
. Spiriferide, containing Uncites, Retzia, Athyris, and Spiri- 
fera. 
Terebratulide, containing Thecidium, Argiope, Terebratella, 
and Terebratula. 
