They are the starfish proper, and have the typical genus Asterias.
The genus is associated with one long extinct in Europe.
By early writers the word was generally given as an equivalent of the Linnaean Loxia, but that genus has been found to include many forms not now placed in the same family.
Amphitherium, of the Stonesfield Slate, typifies the family Amphitheriidae, which includes the American Dryolestes, and in which some would class the European Purbeck genus Amblotherium, although Professor H.
The genus Pyrophorus contains about ninety species, and is entirely confined to America and the West Indies, ranging from the southern United States to Argentina and Chile.