409 



Costa Rica Miocenk — Oi^sson 237 



The fossil shells from Costa Rica are generally more like the 

 West Coast alternata, but are smaller and with somewhat more 

 pointed beaks. The species is also found as fossil, in Santo Do- 

 mingo, Trinidad and Venezuela. 



Gatun Stage: Gatun, C. Z. 



Zone E. Saury Creek, C. R. 



Pitaria Hiliii Dall, var. musanica, n. var, Plate 31, figure 5 



Shell elongate, moderately convex and rather solid; beaks 

 situated at the anterior with the anterior extremity widely 

 rounded but obtusely pointed posteriorly; lunule small, ridged 

 in the middle and defined by a faint line; posterior-dorsal area 

 broad and flat; surface of the shell sculptured with low, irregu- 

 lar, rounded, concentric ribs, which are persistent along the 

 posterior-dorsal slope but lacking elsewhere near^the ventral mar- 

 gin; interior of shell unknown. 



Length 42, height 27, thickness (left valve) 10.50 mm. 



This species has a solid shell like that of Macrocallista. It 

 differs from the true Hillii described by Dall from the Gatun of 

 the Canal Zone, by its more rude and irregular concentric sculp- 

 ture. 



The P. planivieta Guppy, from the Miocene of Jamaica and 

 Santo Domingo is a much {shorter and more regularly sculptur- 

 ed shell. 



Gatun Stage: Hill No. 2, Banajia River ^ C. R. 



Pitaria Guppyana Gabb Plate 31, figure 11 



Caryatis Guppyana Gabb, 1881, Journ. Acad. Nat. Sci. Phila., 2nd 

 series, vol. 8, p. 373, pi. 47, fig. 73. 



Shell small, ovate, moderately convex and porcellaneous; 

 dorsal side straight; ventral side gently convex; posterior ex- 

 tremity sub-truncate but wide, meeting the dorsal side nearly at 

 right angles; anterior extremity much narrower, produced and 

 rounded; lunule narrowly lanceolate, sculptured with the con- 



