188 



Bulletin 39 



360 



Length 39, height 23.5, semi-diameter 11 mm (lest valve) 

 36.5 23 12 (left valve) 



34 23 II (right valve) 



In general form, quite similiar to the Area dariensis Brown 

 and Pilsbry, but distinguished mainly by its simple, undivided 

 ribs. It is also a more convex shell, w^ith higher and more 

 prominent umbos. It differs from Gabb's figure of A. oronlen- 

 sis in its more anterior umbos. 



It is a common species, occurring in zones in the Gatun 

 sandstone of Hone Walk Creek of Eastern Costa Rica. 



Gatun Stage: Hone Walk Creek. 



Area golfoyaquensis Maury, var. medioamericana, n. var. 



Plate 23, figures 4-6 



cf. Area golfoyaquensis Maury, 1917, Amer. Pal., vol. 5, p. 332, pi. 28, 

 fig- 5. 



? Area {Andara) eo7isobrinaQa.'bh, 1881, Journ. Acad. Nat, Sci. Phila., 

 2nd series, vol. 8, p. 378. 



The Area golfoyaquensis was described by Dr. Maury from 

 the Gurabo and Cercado formation of Santo Domingo. It is 

 closel}^ related to the Area Heneke7ii Maur}^, (the Area eojtsob- 

 rina) differing mainly in form. 



The Costa Rican shells are very similiar to Dr. Maury's 

 t3^pe specimens of golfoyaqiiensis, but differ in having 35 instead 

 of 38 ribs, a higher shell, fuller umbos and sharper ribs on the 

 posterior-dorsal area. The central ribs of the left valve are ele- 

 gantly beaded with their interspaces evenly sculptured with 

 raised concentric threads. On the right valve, the ribs are more 

 smooth but their interspaces are similiarly sculptured to those of 

 the left. The ribs of the posterior- dorsal angle of both valves 

 become divided ventrall}^ by 2 or 3 fine threads. The posterior 

 extremity is straight, meeting the hinge-line at an angle of 

 nearly 120 degrees. 



Length 54, height 34, diameter 34 mm. 



