FROM PLIOCENE CLAY BEDS IN COSTA RICA. 367 



VITRINELLA, C. B. Adams. 

 V. PARVA, C. B. Ad., Cab. Panama Shells, 187. 



I have identified the Costa Eican fossil by direct comparison with authentic 

 specimens, presented by Adams to the museum of the Philadelphia Academy. 

 The shell is now living in the Pacific, Mazatlan to Panama. 



V. TRTJNCATA, Gabb, n. s., PI. 4Y, fig. 65. 



Shell minute, discoidal, whorls four; the top abruptly flattened, so that the 

 spire is not visible from a top view ; the flattening being bordered by a sharp angle 

 below which the side of the shell expands convexly, and continues with a gentle 

 curve to the angular margin of the umbilicus. Umbilicus very broad and bordered 

 by an angle similar to, but not so marked as that on the upper margin. Entire 

 surface, including that of the umbilicus, covered with minute revolving lines; these 

 are crossed on the outer side of the whorl by lines of growth. 



Diameter between 1 and 1| mm. 



The angular top and the spiral lines running in true spiral, and not obliquely, 

 will distinguish this from the following species. 



T. OBLIQUESTRIATA, Gabb, 11. s., PI. 47, fig. 66. 



Shell minute, flattened above; spire low; whorls four, slightly convex on their 

 upper surfaces, rounding down to the suture. On top of the body whorl, a little 

 removed from its inner edge, is a slight depression; sides convex; base sloping 

 convexly to the umbilical border. Umbilicus moderately broad, deep, showing 

 all the volutions. Mouth nearly round; inner lip slightly thickened. Surface, 

 besides a few lines of growth, marked by minute revolving striee. Some of these, 

 on the upper surface, begin at the suture, and diverge at a small angle, thus throw- 

 ing out the striation of the top of the whorls obliquely. 



Diameter 2 mm. 



The higher shell and the absence of the angular top, as stated above, are suffi- 

 cient diagnostic characters. 



Y. CRASSicosTA, Gabb, n. s., PI. 47, fig. 67. 



Shell very minute, flattened above so that the apex cannot be seen from a 

 lateral view; whorls three or four; suture pronounced and bordered in the larger 

 whorls by a slightly crenulated border; top of whorl undulated; convex for the 

 inner half, concave on the outer half, and ending in an elevated angle, which 

 forms the upper of three large ribs on the vertical side of the whorl. Base of 

 whorl equally divided by a prominent revolving angle, outside of which it slopes 



