ARNOLD — THE PALEONTOLOGY AND STRATIOKAPHY OF SAN PEDRO. 177 



by smaller pallial sinus, lack of ridge between cartilage-pit and anterior ligamental 

 groove, and by the interior radiating ridges and nairower anterior end. Specimens 

 identified by Dr. Dall. 



Found in the lower San Pedro series at San Pedro and Deadman Island; and 

 in the upper San Pedro series at San Pedro, Deadman Island, Crawfish George's 

 and Los Cerritos. Also found in Pleistocene at Spanish Bight, San Diego. The 

 specimen figured is from the upper San Pedro series at San Pedro, and is now in the 

 collection of Delos Arnold. 



Living. — Kodiak, Alaska, to San Diego (Cooper). 



Pleistocene. — San Pedro (Arnold): San Diego (Cooper; Arnold). 



Pliocene. — Eagle Prairie, Humboldt County; Kirker's Pass, Contra Costa 

 County (Cooper). 



Miocene. — Martinez; Half Moon Bay, San Mateo County; Sunol, Alameda 

 County; Siebeck's, Santa Clara County; Griswold's, San Benito County; Foxiu's, 

 Santa Barbara County; Santiago, Los Angeles County (Cooper). 



Subfamily PTEROPSIDIN.E. 



Genus Labiosa {Schmidt) MMlcr. 



Shell large, thin, inflated, broad and gaping behind, beaks adjacent; surface concentrically 

 striate; dorsal areas well defined; pallial sinus short, rounded, wide; ligament marginal, set off by a 

 prominent lamina of shell from the pit; a single obsolete and very short lateral in each valve before 

 and behind the pit; hinge-plate flattish behind, depressed and excavated in front. 



Tyjie, Mactra anatina Spengler. 



Subgenus Rceta Gray. 



Shell acutely rostrate behind; dorsal areas obscure, the surface of the valves more or less 

 vermiculate; pallial sinus deep, narrow, pointed; ligament submerged, except at the anterior end, 

 set off by a shelly ridge which roofs the apex of the pit, and partially supports the posterior arm of 

 the cardinal tooth; left cardinal small; right cardinal with anus coalescent above; a single anterior 

 and posterior lateral in each valve. 



Type, Lutraria canaliculata Say. 



129. Labiosa (Raeta) undulata Gouhl. 



Lutraria icndulafa Gld. , Proc. Bost. Soc. Nat. Hist., Vol. IV, 1851, p. 89; Bost. Jour. Nat. Hist., 



Vol. VI, 1853, p. 391. PI. XV, fig. 7. 

 Rata undulaia Gld., Carpenter, Brit. Assn. Rept., 1863, p. 640. 

 Lutra'ia transmontana CoN. {,fide Cooper, 7th Ann. Rept. Cal. St. Min., 188S, p. 247) [in part]. 



.Shell of medium size, ovate, ventricose, thin; beaks a little anterior to center; anterior 

 broadly rounded and tumid; posterior narrowed, compressed and acutely rounded, the dorsal margin 

 being a rectilinear slope, gaping; surface concentrically undulated; cardinal tooth strong; posterior 

 lateral tooth small. 



( 23) 5Iarch4. 1903. 



