﻿NEW SPECIES OF -FOSSIL SHELLS FROM PANAMA AND 



COSTA RICA * 



Collected by D. F. MacDonald 

 By WILLIAM HEALEY DALL 



After the appointment of Mr. D. F. MacDonald as geologist to 

 the Canal Commission, the collecting of the Tertiary fossils, so 

 abundant in the Zone, was begun with energy. Amongst the material 

 forwarded was a considerable amount of Pleistocene remains, 

 chiefly from near Toro Point, Monkey Hill (Mt. Hope of some 

 authorities), and the swamps about Limon Bay. All of this deposit 

 was elevated but a few feet above the sea. While mostly composed 

 of common Caribbean recent species there is also an interesting 

 admixture of forms now living only on the Pacific Coast, such as 

 Northia northice Gray, and Pecten (Plagioctenium) vcntricosus 

 Sowerby. Their presence shows that after the complete separation 

 of the two seas a few of the Pacific species lingered on the Atlantic 

 side nearly to the present epoch. The relative proportion of such 

 species was greater in the Pliocene, while in the Oligocene connection 

 between the two oceans was probably intimate, and many of the 

 species are common to both slopes of the present isthmus. 



Subsequent collections by Messrs. Vaughan and MacDonald have 

 not greatly increased the list of those found in the earlier Pleisto- 

 cene collections. 



There is a certain number of species not identifiable with known 

 recent species of the Caribbean waters, yet it would be rash to con- 

 clude that they are extinct. Almost nothing has been done to 

 explore the waters in the vicinity of Colon for mollusks and it may 

 well happen that when the dredge is used there most of the species 

 described in this paper will be found in a living state. While the 

 final report with illustrations may be somewhat delayed, it was 

 thought best to describe these apparently new forms from the Pleis- 

 tocene at the present time. 



YOLDIA PERPROTRACTA, new species 



Shell thin, elongate, inequilateral, rather bluntly pointed at the 

 posterior, and more rounded at the anterior end ; beaks depressed, 



Published by permission of the Director of the U. S. Geological Survey. 

 Smithsonian Miscellaneous Collections, Vol. 59, No. 2 



