Paleontologv Zorkitos Formation 169 



restricted subgenus. Ractiua lacks the prominent posterior 

 lateral. 



L. gardncrac differs from L. gcibbi Pilsbry and Johnson, 

 in having finer concentric undulations, in being less pro- 

 duced and more acutely angulate posteriorly, and in lacking 

 the flat base characteristic of that species. 



Upper Zorritos. Quebrada de las Alturas. 



Labiosa (Racial vcntricosa n. sp. 

 Plate X— Fig. 11. 



Shell high, short, ventricose. highly inflated. Anterior 

 margin rounded, descending abruptly to a broad angulation. 

 from which the posterior ventral margin ascends rather 

 abruptly to the posterior marginal angle, which is approxi- 

 mately a right angle. Posterior dorsal margin straight. 

 Umbones pointed, situated just before the median line, 

 constricted, erect, distinctly episthogyrate. Anterior surface 

 convex. A submedian keel, sharp on the beaks, and broader 

 below, extends from the beaks to the broad ventral marginal 

 angle. The posterior surface is attenuate, as is characteristic 

 of the genus. Sculpture of strong, sharp concentric plica- 

 tions. Hinge and interior unknown. Length. 39; height. 42; 

 diameter, 28 mm. 



This interesting Racta is closer to L. canalicnlata Say ^^^ 

 from the Miocene and later of Xorth Carolina and sur- 

 rounding regions, than are the other two from the Zorritos. 

 but differs from caiiahculata in having more erect beaks, 

 and in being shorter and much more ventricose. 



The specimens studied occur in a lot of unsorted material 

 from Zorritos in Xelson's collection, and although an exact 

 locality label is lacking, their presence with specimens of 

 both gabbi and gardiicrac in the same peculiar matrix makes 

 it likely that they came from the Upper Zorritos formation. 



''"Jour. Ac. Xat. Sc . Phila.. vol. 2, p. 310, 182 1 ; (as Lutraria 

 canalicnlata) . 



