238 



Bulletin 39 



tinuation of the concentric ribs and separated from the shell disk 

 by an impressed line; surface of disk sculptured with rather wide, 

 low or appressed ribs formed between incised lines, but the 

 shell as a whole is porcellaneous and smooth; as the ribs pass 

 over the dorsal-posterior area towards the dorsal margin they 

 decrease in number through fusion; interior concealed in a hard 

 matrix. 



Length 32, height 18, diameter (right valve) 5 mm. 



A small species of the coralline limestones and marls of the 

 lyimon Peninsula, from which it was described by Gabb. It 

 approaches the P.planivieta Guppy of the Miocene of Jamaica and 

 Santo Domingo but is smaller and more rectangular in outlines. 

 It is rather convex with a smooth and polished surface and with 

 regular, even, concentric ribs. 



Gatmi Stage: Port Limon. 



Pitaria VanWInkleaB, n. sp. Plate 32, figure 2, 3 



Shell elongate, depressed; anterior extremity broadly round- 

 ed, posterior more acute; lunule small, lanceolate and defined by 

 an impressed line ; escutcheon long and ver}' narrow; surface 

 sculptured with narrow, closely spaced and reflected ribs; these 

 ribs which number about 100 on the shell disk are even on the 

 center of the shell, but generally uneven on the anterior extrem- 

 ity; the ribs are continuous from the edge of the escutcheon to 

 the anterior dorsal margin; the rounded posterior dorsal slope 

 carries two small, faint rows along which the concentric ribs are 

 slightly higher and occasionally raised into small incipient 

 spines. 



Length 41.5, height 32, diameter (left valve) 10 mm. 



This species is quite similiar to the P. rosea Broderip and 

 Sowerby of the West Coast in its depressed shell and general 

 form. The concentric ribs are very regular, even and continu- 

 ous across the entire surface of the shell. Where these ribs cross 

 the posterior-dorsal slope, they occasionally become raised into 



