194 



Bulletin 39 



366 



terstitial thread iu the interspaces of its right valve. It is nam- 

 ed for Dr. Henr}^ Hinds, formerl}^ of the United States Geologi- 

 cal Survey and the Exploration Department of the Sinclair Con- 

 solidated Oil Corporation. 



Gatiin Stage: Hill No. j, Banayia River. 



Zojie E, Saurj' C7''eek. 



Coll. I, East Grape Point Creek. 



Coll. J, East Grape Point Creek. 



Rio Be ley. 



Subgenus NOETIA, Gray 



Area MacDonaldi Dall Plate 25, figures 4-7 



Area {Noetia) MacDonaldi Dall, 191 2, Smith, Misc. Coll., vol, 59, No. 

 2, p. 9- 



This large Noetia, is very common and characteristic of the 

 Gatun formation in many parts of Northern Costa Rica, and 

 large specimens may reach a length and height of 55 mm or 

 more. It was originally described by Dall from specimens col- 

 lected by Pittier and MacDonald from the Gatun beds of the 

 Banana River, where it is associated with Area Pittieri and is 

 very abundant. 



Two forms or varieties may be recognized. In typical Mac- 

 Donaldi, the shell is high, trigonal, with elevated, narrow mnbos 

 and a prodvcted anterior extremity . The beaks are separated from 

 the hinge-line by a wide ligameyital area. This is the common 

 form along the Banana River. Frequently associated with typi- 

 cal MacDonaldi are shells with a more rectajigular outline, lower 

 but wide umbos. The beaks are close to the hinge line so that 

 the ligme^ital area is narrow. These two types have a very dif- 

 ferent appearance but seem to be connected by transitional forms. 

 To the last variety, I propose the name of subreversa. 



Among recent shells, the Area MacDonaldi finds its closest 

 relation with the common Area reversa Sowerby of the Pacific 

 coast of Central America. 



