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University of California Publications in Geology [Vol. 13 



Family Ostreidae 

 Genus OSTREA Linnaeus 

 OSTEEA CBESCENTICA, n. sp. 

 Plate 26, figures 3 and 4 



Type specimen 12318, Coll. Invert. Palae., Univ. Calif., loe. 2166. 



Shell thick, rugose; upper valve with a pronounced ridge extending from 

 the umbones to the ventral margin. Muscle scars not shown on the type. Length 

 of type, 60 mm.; height, 68 mm.; diameter, 20 mm. 



This oyster resembles 0. skidgatensis Whiteaves and may later be 

 found to fall within the range of variation of that species. 

 Horizon. — Chico group, all three zones. 



OSTEEA TAXIDONTA, n. sp. 

 Plate 26, figure 2 



Type specimen 12317, Coll. Invert. Palae., Univ. Calif., loc. 2167. 



Shell small, thin, irregular in shape; beaks turned anteriorly. Ligamental 

 pit long and shallow; posterior' internal margin of the shell denticulated near 

 the beaks. Length of type, 25 mm.; height, 37 mm.; convexity, 8 mm. 



Specimens from the same collecting locality indicate that this oyster 

 has several points in common with the Recent form 0. lurida Car- 

 penter. The denticulations observed on the Cretaceous species, num- 

 bering about twenty, represent a primitive condition of the provin- 

 culum that is also retained by the Recent species. 0. acutirostris 

 Stoliezka also resembles this California species. 



Horizon. — Chico group, all three zones. 



Genus EXOGYRA Say 

 EXOGYEA INOENATA, n. sp. 

 Plate 27, figure 1 



Type specimen 12284, Coll. Invert. Palae., Univ. Calif., loc. 2143. 



Shell small, rather thin, smooth, very tumid, somewhat elliptical in outline;, 

 beaks large, conspicuously twisted; lower valve of the cotype is roughly circular, 

 irregular, margins smooth. The upper valve of the cotype is similar to that of 

 the type. Height of the type, about 35 mm.; length, about 25 mm. 



Horizon. — Chico group, Actaeonella oviformis zone. 



