Bulletin 39 360 



Ivength 39, height 23.5, semi-diameter 11 m.m (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 mainl}^ by its simple, undivided 

 ribs. It is also a more convex shell, with 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- 

 1 Area {Andara) cojisobji na Gahb, 1881, Journ. Acad. Nat. Sci. Phila., 



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



The Area golfoyaquensis was described hy Dr. Maurj^ from 

 the Gurabo and Cercado formation of Santo Domingo. It is 

 closel}^ related to the Ajxa Henekeni Maury, (the Area eonsob- 

 riua) differing mainly in form. 



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

 \.Y'^^s\^^civa&a.soi golfoyaquensis, 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 similiarl}^ sculptured to those of 

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

 become divided ventralb/ 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. 



