PALEONTOLOGY ZORRITOS FORMATION 121 



Santo Domingo. Maury's figure shows an anterior sinus in 

 the left valve ; this does not exist in nelsoni } and the granu- 

 lation of the ribs is coarser in chiriquiensis. The area of 

 nelsoni is lower and the teeth are larger. Otherwise the two 

 are closely similar. 



A. nelsoni shows close relationship to two European 

 forms, Anadara diluvii var. bollenensis (Fantannes) 121 and 

 A. nchteli (Deshayes), 122 which Sacco has described from 

 the Tertiary of Italy. A. diluvii, which ranges from the 

 Helvetien to the Astien, has apparently about the same num- 

 ber of ribs, and is in other features entirely similar except 

 that the beaks of nelsoni are a bit higher, and the area some- 

 what shorter, with the result that the posterior margin of 

 nelsoni meets the hinge at an angle greater than in Sacco's 

 form. A. nchteli, from the Helvetien and Tortonien of the 

 Piedmont, is also similar, but its ribs are broader in propor- 

 tion to the interspaces. The area is shorter in nelsoni. 

 According to figures given by Hoernes 123 the furrows in 

 nchteli are more numerous, more evenly spaced, and less 

 sharply V-shaped than in nelsoni. Areas of this type ap- 

 parently did not appear in Europe until the Helvetien. They 

 were present in the Caribbean and adjacent regions at least 

 as early as late Oligocene. 



Upper Zorritos. Quebradas del Toro and del Grille. 



Area (Anadara) toroensis n. sp. 

 PLATE VI Figs. 9, 10; PLATE VII Fig. i. 



Shell large, heavy, inflated. Anterior margin broadly 

 rounded, forming a right angle with the hinge-line ; ventral 

 margin gently rounded, its flattest part being usually nearly 

 parallel to the hinge-line, in some specimens descending 

 slightly posteriorly. Posterior margin produced and rounded 



121 Piemonte, pte. 26, p. 22, pi. 4, fig. 13, 1898. 



122 Ibid., p. 23, pi. 5, figs. 2-8. 



123 Abh. k.k. geol. Reichs., Bd. 4, p. 331, pi. 43, figs. 3, 4, 5, 1870. 



