80 ORIGIN OF THE WEST INDIAN ECHINID FAUNA. 



In order to show the former distribution of the genera of which the Echi- 

 nid Fauna of the West Indies is made up, Ave must trace as far as possible the 

 origin of these 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 bad 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 tbe same oceans. 



Hemipedina, 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 Pygasler relictus is only tbe 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, Rhynchopygus, Pourtalesia, 

 Ileiniaster. and Periaster. 



Of these genera, Temnechinus, Echinus, Hemiaster, and Periaster already 

 bad during tbe Tertiary as extensive a geographical range as to-day. At 

 the present time, Echinus extends over the Atlantic, tbe Indian, and the 

 Pacific Oceans ; Temnechinus is a tropical Atlantic and Pacific genus ; 

 Hemiaster is characteristic of tbe Atlantic and of tbe Nortb Pacific, Peri- 

 aster of the East American tropical Atlantic and tropical Pacific, and Rhyn- 

 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 far 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, Ethinobrissus, lhis- 

 Bopsis, Agassi/.ia. 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- 



