PALEONTOLOGY ZORRITOS FORMATION 149 



of large specimen, 48.5; height, 42; (semi) diameter, 14 

 mm. Smaller specimen, length, 30.5; height, 25.5; (semi) 

 diameter, about 8 mm. 



Lower Zorritos, Variegated. Quebrada Zapotal. 



Pitaria (Lamclliconcha) com var. aequicincta n. var. 

 PLATE IX Figs. 6, 7. 



Shell thin, large, somewhat compressed. Anterior margin 

 broadly rounded; ventral margin elliptical, its juncture with 

 the posterior margin in the form of an apically rounded 

 acute angle. Surface generally convex, but the shell is not 

 highly inflated. Sculpture of fine, nearly even concentric 

 ribs, which are slightly steeper on their dorsal slopes, and 

 which appear very finely and sharply graven. There is no 

 radial striation. The cardinal areas are poorly defined. Inner 

 shell unknown except that the anterior muscle scar is but 

 slightly impressed, the posterior not at all, and that the 

 inner valve-margins are smooth. Length (large specimen) 

 49.5; height 38; (semi) diameter 10 mm. Length (smaller 

 specimen) 31.5; height ?; (semi) diameter 6 mm. 



Two casts, one with perfectly preserved portions of the 

 shell remaining, represent this variety in the Zorritos col- 

 lection. In outline and type of sculpture it agrees well with 

 Pitaria cora Brown and Pilsbry, 166 from Gatun, but cora 

 is a fuller shell, being much more inflated, and having the 

 muscle scars and pallial line much more deeply impressed. 



The Zorritos variety appears further to attain a larger 

 size. As noted by Brown and Pilsbry (loc. cit.), Pitaria 

 hillii D'all, 167 from the Gatun formation, is a longer, lower 

 form. In sculpture, however, it is entirely similar, and its 

 relationship to both cora and the variety aequicincta is close. 

 P. cercadica Maury, 168 from the lower horizon in -the 



l68 Proc. Ac. Nat. Sc. Phila., vol. 63, p. 370, pi. 28, fig. 3, 1911. 

 187 Trans. Wag. Inst, vol. 3, pt. 6, p. 1268, pi. 54, fig. 7, 1903. 

 168 Bull. Amer. Pal., vol. 5, No. 29, p. 216, pi. 37, fig. 10, 1917. 



