2o8 



Bulletin 39 



380 



Spondylns gumanomocon Brown and Pilsbry, 1912, Proc, Acad. Nat. 



Sci. Phila., vol. 14, p. 514, footnote. 

 Spondylus gumanomocon Maury, 1917, Bull. Amer. Pat., vol, 5, p. 



355. 



This is a species with very unequal valves, that of the left 

 or upper, being small, pectiniform and lacking in a cardinal 

 area, while the right or lower valve is strongly convex, with a 

 high produced beak and a high cardinal area. The sculpture of 

 the two valves is similiar, except that the umbo of the right is 

 strongly foliaceous. It occurs in the Miocene of Santo Domin- 

 go, where it was referred to the recent S. americanus by Gabb. 



Gatun Stage: Coll. 2, Hojie Walk Creek. 

 Port Li7non. 



Genus PLICATULA, Lamarck 

 Plicatula marginata Say Plate 28, figures 6, 7 



Plicatula marginata Say, 1824, Journ. Acad. Nat. Sci. Phila., vol. 4, 



pp. 136-137, pi. 9, fig. 4. 

 Plicatula marginata Dall, 1898, Trans. Wagner Free Inst. Sci., vol. 3, 



pt. 4, p. 764. 



The Panama and Costa Rican examples are not typical but 

 they approach more closely the Plicatula marginata Say than 

 they do the densata which Dall has recorded from the Bowden 

 beds of Jamica. 



The shells vary from subcircular to elongate and in some 

 cases carry the dark, marginal band so frequently seen in typical 

 marginata. The ribs number five to seven; the shells with more 

 rounded form and more numerous ribs suggest the densata, but 

 the ribs are higher and more foliaceous, and can be exactly du- 

 plicated by scores of true marginata in the Cornell collection. 

 The above determination must however be considered as purely 

 provisional at the present time. 



The typical P. densata was described by Conrad from the 

 lower Chesapeake Miocene of New Jersey, but it also occurs in 



