120 FOSSIL ECHINI OF THE WEST INDIES. 



All other species on the list may be of Miocene age, but additional 

 information is needed before a definite opinion is warranted. 



The few species of Miocene echinoids known from the West Indies is 

 rather surprising, because the number of species of Miocene organisms 

 is probably as much as ten times more than all of those from the Eocene 

 and Oligocene formations combined. The sediments of the different 

 epochs are different. The Eocene and Oligocene deposits are largely 

 calcareous and contain organisms of reef facies, viz, corals, calcareous 

 algse, large Foraminifera such as Orthophragmina, Lepidocyclina, 

 and Operculina, incrusting Bryozoa, and echinoids. The Miocene 

 strata as a rule are less calcareous and more arenaceous or argillaceous, 

 and are exceedingly rich in species of mollusca, the number of species 

 of this group probably exceeding 2,000; there are many species of 

 smaller Foraminifera and Bryozoa, and simple corals are abundant. 

 But in some places there are calcareous Miocene strata, and when 

 they are searched for echinoids they may yield additions to the Miocene 

 echinoid faunas. 



These quantitative relations of the echinoids to the mollusks hold 

 true also in the United States. Echinoids are most abundant in the 

 Ocala limestone, of upper Eocene age, approximately contempora- 

 neous with the St. Bartholomew limestone ; there are a few common 

 species in the Oligocene (Vicksburg group and Chattahoochee forma- 

 tion) ; but they are very rare in the Miocene, in striking contrast to 

 the great profusion of mollusks in the Alum Bluff and Choctawhatchee 

 formations. 



The following are the names of the known Miocene echinoids from 

 Panama and Costa Rica : 



Clypeaster gatuni Jackson. 1 Miocene, Gatun formation, station 5662, near Gatun Dam 



site; and upper Oligocene, Emperador limestone at station 6237, north of Ancon 



Hill, about 4 miles south of Diablo ridge. 

 Encope annectans Jackson. 1 Miocene, Gatun formation, station 5846, Spillway, Gatun 



Dam. 

 Encope platytala Jackson. 1 Miocene, Gatun formation, station 6029a, 0.25 to 0.5 mile 



from Camp Cotton, toward Monte Lirio. 

 Encope megatrema Jackson. 1 Miocene, Gatun formation, station 6030, about 1.5 miles 



from Camp Cotton, toward Monte Lirio. 

 Encope gatunensis Toula. 2 Miocene, Gatun formation. 

 Schizaster armiger W. B. Clark. 1 Miocene (?), Bonilla, Costa Rica. 

 Schizaster cristaius Jackson. 1 Miocene (?), Brazil, Costa Rica, station 5505. 

 Schizaster panamensis Jackson. 1 Miocene, Gatun formation, near Gatun, stations 6008 



and 7294. 



1 Jackson, R. T., Fossil Echini of the Panama Canal Zone and Costa Rica: U. S. Nat. Mus. 

 Bull. 103, pp. 103-116, I, pis. 46-52, 1918. 



2 Toula, Franz, Die jung-tertiare Fauna von Gatun am Panama Kanal: Geolog. Reichs- 

 Anstalt, Wien, vol. 61, pp. 487-530, pis. 30-31, 1911. 



