80 ORIGIN OF THE WEST INDIAN ECHINTD FAUNA. 
In order to show the former distribution of the genera of which the Echi- 
nid Fauna of the West Indies is made up, we must trace as far as possible the 
origin of tliese genera. We find at the outset a few old genera, like Cidaris, 
Dorocidaris, Porocidaris, and Salenia, dating back to the Jurassic period, and 
which already in the Tertiary had probably as extensive a geographical 
distribution as at the present day. Dorocidaris and Porocidaris at the pres- 
ent time are Atlantic and Indo-Pacific genera, while Salenia and Cidaris are 
confined to the warmer belts of the same oceans. 
Heniipedina, which dates back to the Jura, is found fossil in the Tertiary 
of North America, and has thus far not been dredged outside of the Carib- 
bean Fauna. Pygaster is also a Jurassic genus, but it is most probable that 
the Pi/ffusier relidus is only the young of one of the West Indian Spatan- 
goids with an ancient facies, as has been suggested by De Loriol. The 
genera which date back to the Cretaceous period, either actually or by 
closely allied genera, are Podocidaris, Asthenosoma, Phormosoma, Tem- 
nechinus, Echinus, Echinocyamus, Conoclypus, Pihynchopygus, Pourtalesia, 
Hemiaster, and Periaster. 
Of these genera, Temnechinus, Echinus, Hemiaster, and Periaster already 
had during the Tertiary as extensive a geographical range as to-day. At 
the present time, Echinus extends over the Atlantic, the Indian, and the 
Pacific Oceans ; Temnechinus is a tropical Atlantic and Pacific genus ; 
Hemiaster is characteristic of the Atlantic and of the North Pacific, Peri- 
aster of the East American tropical Atlantic and tropical Pacific, and Ehyn- 
chopygus appears limited to-day to the American faunal districts of the 
same oceans, although it has been found in the Tertiaries of Australia and of 
Europe. Nothing is known of the distribution during the Tertiary of the 
Atlantic and Pacific genera Pourtalesia, Asthenosoma, and Phormosoma. 
Podocidaris is a tropical Atlantic and Pacific genus. Echinocyamus extends 
in the North Atlantic to within the tropics. 
The genera dating back to the earlier Tertiary period include by flir the 
greater number of the genera of the West Indian Fauna ; they are Coelo- 
pleurus, Strongylocentrotus, Trigonocidaris, Toxopneustes, Hipponoe, Clype- 
aster, Echinanthus, Echinoneus, Neolampas, Echinolampas, Homolampas, 
Paleopneustes, Linopneustes, Spatangus, Echinocardium, Rhinobrissus, Bris- 
sopsis, Agassizia, Brissus, Metalia, Meoma, Macropneustes, Schizaster, and 
Moira. Of these the genera extending in the equatorial belt of the Atlantic 
and Indo-Pacific region are Trigonocidaris, Toxopneustes, Hipponoe, Clype- 
