i68 Studies in Geology, No. 3 



and Johnson's types from the Dominican RepubHc, with the 

 exception that the ribs of the Peruvian form are not as 

 much weakened centrally as in the Domingan gabbi. These 

 differences are barely perceptible, and can not be held to 

 have systematic value. 



Upper Zorritos. Quebrada de las Alturas. 



Labiosa (Raeta) gardnerae n. sp. 

 Plate X — Fig. 10. 



Shell small, anteriorly inflated, very thin, subtrigonal in 

 outline. Anterior margin broadly rounded ; ventral margin 

 elliptical, ascending rather sharply to the posterior marginal 

 angle, which is less than a right angle ; posterior-dorsal 

 margin nearly straight. Umbones small, inflated, pointed, 

 incline slightly backward, prosogyrate. Anterior surface 

 highly convex, with a suggestion of a carina. Posterior 

 surface attenuate, flattened, with a slight broad concavity 

 halfway between the beaks and the marginal angle. Sculp- 

 ture of concentric plications, externally sharp at the top 

 and with concave slopes, about equal in declivity dorsally 

 and ventrally ; interspaces comparatively broad, U-shaped. 

 Hinge not known. Length, 28.5; height, 23.5; (semi) diam. 

 about 8 mm. 



This species is similar in general apj^earance to L. canal- 

 iculata Say,^°-^ from the Miocene and later of the Atlantic 

 Coast. It differs, however, in being much smaller, with more 

 erect beaks and proportionally more as well as finer con- 

 centric undulations. It differs from the recent Raeta (Rae- 

 tina) Iiidica Dall ^"^ in being less produced posteriorly, and 

 in the sharper ascent or its ventral margin. It is much 

 smaller than the species characteristic of the subgenus Raeta 

 S.S., and in point of size it corresponds more nearly to the 

 section Ractina Dall ; but the ventral margin ascends sharply, 



"■'Jour. Ac. Nat. Sci. Phila., vol. 2, p. 310. 1821 ; (as Lutraria 

 canaliciilata) . 



"'Trans. Wag. Inst., vol. 3, pt. 4, p. 882, 1898. 



