ORIGIIf OF THE WEST INDIAN ECHINID FAUNA. 
81 
aster, Echinanthus, Echinolaiiipas, Homolampas, Paleopnenstes, Linopneustes, 
Rhinobrissus, Brissus, and Metalia. The genera having an Atlantic and 
Pacific range are Strongjlocentrotus, Spatangus, Echinocardiuni, Brissopsis, 
and Schizaster. Leaving only with a more or less limited range Coelopleuriis, 
found in the Caribbean, Indian Ocean, and East Indian Archipelago, and 
with nearly the same distribution in the Tertiary, having only disappeared 
from the Eastern North Atlantic region where it once flourished. Echino- 
nens, Coelopleurus, and Macropneustes have very much the same geographical 
and geological range. Agassizia, Meoma, and Moira are probably 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 Austi'alia. 
The genera dating back only to the later Tertiary period are Arbacia, 
Echinometra, Mellita, and Encope. But little is known of their former geo- 
graphical extension. Echinometra is a tropical Atlantic and Indo-Pacific 
genus ; Arbacia is a tropical Atlantic and Pacific genus, 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, Paloeobris- 
sus, Urechinus, 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 PaloBobrissus, which represents Platybrissns 
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 back to the Cretaceous, and Pateotropus, Palteobrissus, 
Urechinus, and Cystechinus are to-day the old-fashioned representatives of 
the types of Spatangoids which characterized the Cretaceous seas. 
This analysis sliows that the Echinid Fauna of the West Indian seas of to- 
day is made up (1.) of five genera wliich date back to the Jurassic period; 
(2.) of ten genera which go bnck to the Cretaceous period; (3.) of twenty- 
four genera dating from the earlier Tertiary period ; (4.) of only four genera 
characteristic of the later Tertiaries ; (5.) of seven genera which we may 
look upon as the representatives of the Ananchytidoe and Infulasteridae, 
and of the Pseudodiadematidfe of the Cretaceous period. In all these old- 
fashioned genera we find species having a cosmopolitan range. 
* One species of Mellita is said to come from the Red Sea. 
