PALEONTOLOGY ZORRITOS FORMATION 101 



groove and a marginal furrow with universally elevated 

 ridge instead of several furrows and an elevation behind the 

 beak only; the meeting of the valves, which is perfect and 

 not discrepant as in cor-cupidonis; pantheonensis is not as 

 highly inflated, and is somewhat more produced posteriorly. 



Area niicata Guppy, 94 from the Manzanilla beds of Trin- 

 idad, is a much smaller form, but is evidently related. It 

 has, among other features of difference, a larger number of 

 ribs. Area alcinia Dall/ 5 from the Caloosahatchie Pliocene 

 of Florida, represents the next step in the evolution of this 

 type, with the assumption of the characters of the true 

 C linear ca. It is true that alcima itself is on the border-line 

 of the group, but, as Ball (loc. cit.) has pointed out, it has 

 sufficiently well developed the Cunearca hinge, area, and 

 discrepant sculpture to place it in that group. A. larkinii 

 Nelson is similar as pointed out in the description of that 

 species. 



Variegated. Small quebrada south of Quebrada Pantheon. 



Area (Scapharca) zapotalensis n. sp. 

 PLATE V Fig. 10. 



Shell of medium size, moderately inflated, produced pos- 

 teriorly. Anterior margin rounded. Ventral margin broadly 

 curved, descending at a low angle ; posterior margin recurves 

 in a sharp angle, being nearly straight, and forming an 

 angle of about 130 with the hinge. Umbones erect, inflated, 

 somewhat broad. General surface convex except posteriorly, 

 where it is slightly excayated behind the beaks. Valves join 

 posteriorly to form a wedge-like shape. Sculpture of about 

 29 ribs, apparently squarely nodular on the left valve and 

 smoother on the right. Area narrow ; exact characters not 

 visible. Teeth and inner shell not known. Length, 24.5 ; 

 height, 21.5; diam., 18; length of hinge, 15 mm. 



94 Quart. Jour. Geol. Soc. Lond., vol. 22, p. 583, pi. 26, fig. 5, 

 1866. 

 93 Trans. Wag. Inst, vol. 3, pt. 4, p. 635, pi. 31, figs. 5, 7, 1895 



