42i Dominican Sections — Maury 



water at 785 fathoms. The genus Borso?iia is now restricted to 

 the abyssal zone of the Antilles and Brazil. Protocardia islahis- 

 paniolce is represented by the deep sea P. peramabilis. The 

 nearest ally of Sconsia laevigata is 5*. barbudensis, dredged off 

 Barbuda. 



These cases might tempt one to imagine deep sea conditions 

 for our faunas but for the weight of evidence of the shallow 

 water species. We must conclude that the ancestors of these 

 deep sea forms inhabited shallow water and that their descend- 

 ants have since resorted to deep sea life from stress of circum- 

 stances. 



The Pacific and Oriental Elements in the Faunas. — The 

 majority of our molluscan species are the ancestors of species now 

 living in the Antilles. Many have continued on almost without 

 change since the deposition of the blue clays. The Atlantic ele- 

 ment is very strong. Yet certain genera and species are now 

 represented only in the recent faunas of the Pacific coast of the 

 Americas, the Oriental seas and the Indian Ocean. This Pacific 

 and exotic element speaks in favor of the Oligocene age of our 

 fossil faunas, since the western migrants presumably crossed 

 into the Pacific before the closing of the Isthmus at the end of 

 the Oligocene, and clearly the Antillean stock existed prior to 

 that elevation. There are, however, two weak points in this line 

 of reasoning: — (1) Our species may have lived on undisturbed 

 after the Oligocene and so represent a later period of time ; (2) 

 Dr. Vaughan* has suggested a later interocean water way in the 

 Upper Miocene or Pliocene, possibly located in the region of the 

 Isthmus of Tehuantepec. 



Of exotic genera we may mention Surcula, now restricted to 

 the Indian Ocean, Meta found in the Malay archipelago, \Metula 

 in the China seas and off the Cape. Illustration of Pacific species 

 living on the West Coast of the Americas and showing a close 

 kinship to our Dominican fossil shells are Conus pyriformis repre- 

 senting C. recognitus; Ca?icellaria urceolata allied to C. Rowelli ; 



*See Reef Coral Fauna of Carrizo Creek, U. S. G. S. Prof. Paper 98, 

 p. 369, 1917. . 



