PALEONTOLOGY ZORRITOS FORMATION 167 



end ; sculptured with small concentric ribs which are weaker 

 in the middle, where there is a slightly depressed, quite 

 inconspicuous wedge-shaped area radiating from the beaks. 

 Posterior end rounded, somewhat compressed, the contour 

 in dorsal view being somewhat wedge-shaped. Hinge not 

 exposed. Length, 28; alt. 23; diam. 13.8 mm." Pilsbry 

 and Johnson, 1917. 



The shell is small, delicate, moderately inflated, long, 

 somewhat low. Anterior dorsal margin nearly straight, some- 

 what produced; extreme anterior margin rounded; ventral 

 margin almost straight, ascending slightly. Posterior mar- 

 ginal angle blunt, pronounced ; the shell is produced 

 posteriorly. Umbones pointed, prosogyrate, moderately 

 inflated, erect, situated just forward of the middle. Surface 

 generally convex, flatter posteriorly, where the shell is some- 

 what attenuate, and very slightly excavated behind the beaks. 

 Sculpture of prominent, sharp concentric undulations, about 

 4 in the space of 5 mm. on the center of the disc of Zorri- 

 tos specimens. Inner shell unknown. Length, 36; height, 

 27; diameter, 16.5 mm. 



This species is somewhat similar to Raeta (Raetina) 

 indica Dall, 192 but differs in being less produced and more 

 blunt posteriorly, and chiefly in having the posterior lateral 

 tooth, the lack of which is a sectional characteristic of 

 Raetina. It differs from L. gardncrae, in having the wedge- 

 shaped area on the disk, which is not present in gardnerae, 

 and in that the ventral margin does not ascend posteriorly 

 with nearly the sharpness common to gardnerae, with the 

 result that the sculpture of gabbi is biangulate in outline, 

 the ribs being flat ventrally and turned up on either side, 

 whereas that of gardnerae is monangulate, as in canaliculata 

 Say. The posterior marginal angle of gardnerae is much 

 sharper. 



The Zorritos specimens compare very well with Pilsbry 



192 Trans. Wag. Inst, vol. 3, pt. 4, p. 882, li 



