437 Costa Rica Miocene — Olsson 265 



Aladra Xuttallii Reeve, 1854, Conch., Icon., Madra, fig. 125. 

 Labiosa Ihieata Dall, 1898, Trans. Wagner Free Inst. Sci., vol. 3, pt. 

 4, p. 906. 



This species is represented in our collection by fragments of 

 the hinge and a perfect mold of the interior which is figured. 

 This mold compares very closel}' with recent specimens of Labi- 

 osa lineata Say. 



Dall records this species as fossil in the Pliocene Caloosa- 

 hatchie beds of Florida and we have several fragments in the 

 Cornell collection from the Upper Chesapeake Miocene of Nat- 

 ural Well, North Carolina. 



Gatun Stage: Saury creek. 



Coll. 6, Estrella River. 



Genus MULINIA, Gray 

 Muiinia lateralis Say, var. sauryensis, n. var. Plate 28, figures 23. 24 



The species of Midinia are extremlh' variable and we have 

 therefore associated this form with the common lateralis of Say, 

 although it may later prove to be a distinct species. 



The general form of the shell is like corbuloides Deshayes, 

 the common Gulf varietj^ of lateralis of Say. It differs most im- 

 portanth- from lateralis in having the beaks situated a short dist- 

 ance above the hinge-line as is seen in the Chesapeake Miocene 

 M. congesta Conrad. In other characters, the Costa Rican shells 

 are more closeh* related to the lateralis, than to the congesta. 

 The shell is fairly convex and thin. 



Length 20, height 16, semi-diameter 6 mm. 



Gatun Stage: Zone E, Saury creek. 



Genus MESODESMA, Deshayes 

 Mesodesma costaricensis, n. sp. Plate 28, figure 18 



Shell ovate, moderately convex, inequilateral, thin; anterior 



