PALEONTOLOGY ZORRITOS FORMATION 177 



nearly equal, the right being the more inflated, and are 

 equally sculptured. There is neither lunule nor escutcheon. 

 Inner shell unknown. Length, 17.5; height, 10; diameter, 

 7 mm. 



This species is characterized by its very sharp carina, and 

 the distinctly sculptured intercarinal area. In this set of 

 features it is unlike any fossil Cuneo'corbula from the Wes- 

 tern Hemisphere known to the writer. Two European forms 

 have the very acute carina, and one is very close. In exter- 

 nal characters it is similar to C. revoluta Brocchi, 205 and C. 

 basteroti Hoernes, 206 from the lower Oligocene of Germany. 

 C. revoluta is the closer of the two, being indistinguishable 

 but for the sculpture of the intercarinal area, more deeply 

 channelled in acutirostra, the general sculpture, apparently 

 coarser in revoluta, and possibly in the ventral margin, which 

 is obscured by irremovable matrix in the available specimens 

 of acutirostra. C. basteroti is likewise coarser in sculpture, 

 and differs further .in being shorter, with the beaks sub- 

 central in position. 



Comparisons with American species offer less satisfaction 

 because of greater differences, and the selection of related 

 species carries less meaning. C. caimitica Maury, 207 from 

 the Lower Miocene of Santo Domingo, is somewhat similar, 

 but is much shorter, lacks the very sharp carina, has coarser 

 sculpture, and has the prominent carina straight in its upper 

 part, whereas that of acutirostra curves over into the beak. 



Upper Zorritos. South of Quebrada de las Alturas ; Que- 

 brada del Grillo. 



- 05 Abh. k.k. geol. Reichs., Bd. 4, p. 38, pi. 3, fig. 9, 1870. 



200 Ibid., p. 39, pi. 3, fig. 10. 



207 Bull. Amer. Pal., vol. 5, No. 29, p. 233, pi. 39, figs. 18, 19, 1917. 



