* 



Clark: The San Lorenzo Series of Middle California 137 

 Family Thraciidae 



Genus THRACIA Leach 



THEACIA CONDONI Ball 



Plate 11, figure 12; plate 12, figure 2 



Thracia condoni Dall, U. 8. Geol. Surv., Prof, paper no. 59, p. 135, pi. 19, 

 fig. 5, 1909. 



Thracia condoni Dall, Arnold and Hannibal, Proe. Amer. Philos. Soc, vol. 

 52, p. 581, 1913. 



Thracia condoni Dall, Clark, Univ. Calif. Publ., Bull. Dept. Geol., vol. 9, 

 no. 2, pp. 15, 18, 1915. 



Thracia condoni was referred to by Dall as belonging to the 

 Miocene; the type came from Smith's Quarry near Eugene, Oregon. 

 These beds are referred to by Arnold and Hannibal as belonging to 

 their San Lorenzo horizon of the Astoria series. T. condoni is listed 

 by them as being a characteristic species of their San Lorenzo horizon. 

 The writer has seen it from a number of localities of Oregon and 

 Washington ; in every case it was associated with a fauna, considered 

 by him to be Oligocene. 



Genus CYATHODONTA Conrad 

 CYATHODONTA WEAVERI, n. sp. 

 Plate 13, figure 10; plate 14, figure 1 

 Type specimen 11131, Coll. Invert Palae. Univ. Calif., loc. 1131 

 Shell thin, medium in size to fairly large, broadly ovate. Beaks fairly con- 

 spicuous, slightly posterior to the middle. Anterior dorsal margin gently convex, 

 sloping away from the beaks rather steeply ; posterior dorsal margin straight ; 

 anterior end broadly and regularly rounded ; posterior end broadly and squarely 

 truncated; ventral margin regularly and rather strongly arcuate. Surface covered 

 by fairly broad and prominent concentric undulations, on and between which are. 

 finer and somewhat irregular incremental lines; seven of the major undulations 

 can be distinguished on the type. A fairly distinct ridge extends from the beaks 

 to the basal angle of the truncated posterior end ; posterior to this the surface is 

 rather strongly depressed. Muscle scars faint. 



Dimensions. — Type specimen: height, 22.5 mm.; length, 27.5 mm. 



The outline of this species is very similar to that of Thracia trapc- 

 zoides Conrad, 114 a species common in the Oligocene, Miocene and 

 Pliocene of Oregon and Washington, from which it is distinguished by 

 the prominent undulations, characterizing the genus Cyathodonta. 



ii4 For original description of Thracia trapezoides Conrad, see Geol. U. S. 

 Expl. Exped., p. 723, pi. 17, figs. 6a and 66, 1849. For good redescription of this 

 species by Dall, see U. S. Geol. Surv., Prof, paper no. 59, p. 1135, pi. 2, fig. 14; 

 pi. 13, fig. 7, 1909. 



