Vol. VII] DICKERSON— ANCIENT PANAMA CANALS 199 



tially distinct, but six per cent of species being common. Ever- 

 mann and Jenkins"' who studied the problem more in detail 

 recognized 1307 species on the Panama side. Ruling out 16 

 of these owing to their very wide distribution, they determined 

 that approximately 4.3 per cent were common to the two shores. 



Belt.'' a naturalist in Nicaragua, estimates the Caribbean 

 marine molluscan fauna at 1500 species and the Panamic fauna 

 at 1341. Of these, but 50 are common to the two shores. 



A. Agassiz' states that all but three of the Pacific echinoid 

 genera are represented in the Caribbean, but he recognized no 

 common species. Ortmann. who later studied the echinoderms 

 from these two regions, states that even genera and families 

 show a remarkable contrast and that there are no species in 

 common. VerrilP states that no species of corals in these two 

 provinces are identical. Genera and families of reef building 

 corals of the Caribbean Province are, except Porites, absent 

 from the Panamic region whereas Meandrina, Diploria, Mani- 

 cina, Colpophyllia, Agaricia, Siderastrcea (Astrea), Oculina, 

 Madrepora and Millepora are abundant in the Caribbean. 

 Pocillopora, Montipora, Pavonia, are characteristic Pacific 

 genera and do not occur in the Caribbean. From this evidence 

 he concludes that there has been no connection between the 

 Atlantic and Pacific oceans since early Tertiary. 



Brown and Pilsbry^ state that the genera Cymia, Solenos- 

 teira, Stromhina, Malea, Trachycardiiun, of helchcri group, 

 dementia, Acila, Tesseracme, Cadidus, characteristic Bowden 

 genera — none of which is a deep water form — occur in the 

 recent fauna of the Panamic province. None of these genera 

 occurs in the recent Antillean fauna, hence one concludes that 

 the Panamic fauna developed from a Bowden stock of probably 

 early Miocene age. 



Spencer'° postulates Pliocene canals through the Isthmus of 

 Tehuantepec. Bose and Toula^^ who have studied the Isthmus 

 of Tehuantepec, disagree entirely with Spencer's geologic data 

 and state that it is impossible to trace marine terraces across 



^ Evermann, Barton W., and Jenkins, Oliver P., Proc. U. S. Nat. Mus., vol. 14, 

 126, 1891. 



" Belt, Thomas, The Naturalist in Nicaragua. London, 247, 1888. 



'Agassiz, .\., Bull. Mus. Comp. Zool., vol. 1, p. 301, 1869. 



^Verrill, A. E., Proc. Essex Institute, 323, 1866. 



•Pilsbry, H. A., and Brown. A. P., Proc. Acad. Sci. Phila., 1911, 336. 



"> Spencer, J. W.. Bull. Geol. Soc. Amer. vol. 8, 13-34, 1897. 



"Bose, E., and Toula, F., Zur Jungtertiaren Fauna von Tehuantepec, Jahrbuch der 

 kaiserlich-koniglichen Geologischen Reichsanstalt, 215, 1910. 



