ORIGIN OF mi: W I>1 INDIAN ECHINID FAUNA. 81 



aster, Echinanthus, Echinolampas, Eomolampas, Paleopneustes, Linopneusl 

 Rhinobrissus, Brissus, and Metalia. The genera having an Atlantic and 

 Pacific range are Strongylocentrotus, Spatangus, Echinocardium, Brissopsis, 

 and Schizaster. Leaving only with a more or less limited range Ccelopleurus, 

 found in the Caribbean, Indian Ocean, and Easl Indian Archipelago, and 

 with nearly the same distribution in the Tertiary, having only disappeared 

 from the Eastern North Atlantic region where it oner flourished. Echino- 

 neus, Ccelopleurus, and Macropneustes have wry much the same geographical 

 and geological range. Agassizia, Meoma, and Mfoira are probablj strictly 

 tropical American genera, occurring both on the Pacific and Atlantic sides 

 of the continent; but they formerly had a much wider geographical distri- 

 bution, Agassizia having been found in the Tertiary of Egypt and .Meoma 

 in Australia. 



The genera dating back only to the later Tertiary period are Arbacia, 

 Echinometra, Mellita, and Encope. Bui little is known of their former geo- 

 graphical extension. Echinometra is a tropic;, 1 Atlantic and Indo-Pacific 

 -e,,u- Arbacia is a tropical Atlantic and Pacific yen. is. most widely distrib- 

 uted on both sides of the American continent; while .Mellita- and Encope 

 are eminently tropical American, occurring on both sides of the continent. 



This leaves the genera Diadema, Aspidodiadema, Palaeotropus, Palaeobris- 

 bus 3 Qrechinus, Cystechinus, and Aceste, which have as yet not been found 

 fossiL These genera, with the exception of Cystechinus, limited to the 

 Southern Atlantic and Pacific, and Palseobrissus, which represents Platybrissus 

 in the Atlantic, have an extended geographical range in the tropical belt of 

 both the Atlantic and the Pacific Oceans. The nearest allies of Diadema and 

 of Aspidodiadema date Lack to the Cretaceous, and Palaeotropus, Palaeobrissus, 

 Qrechinus, and Cystechinus are to-day the old-fashioned representatives of 

 the types of Spatangoids which characterized the Cretaceous seas. 



This analysis shows that the Echinid Fauna of the West India-,, B ea* of to- 

 day is made up (1.) of live genera which date back to the Jurassic period: 

 of ten genera which go back to the Cretaceous period ; (3.) of twenty- 

 four genera dating from the earlier Tertiary period ; t I.) of .ml\ four genera 

 characteristic of the later Tertiaries; (5.) of seven genera which we may 

 look upon as the representatives of the Ananchytidoe and Infulasteridee, 

 and of the Pseudodiadematidae of the Cretaceous period. In all these old- 

 fashioned genera we find species having a cosmopolitan range. 



ol M. IV... I Sea. 



