422 University of California Publications in Geology [Vol. 13 



Family Spondylidae 

 Genus SPONDYLUS Linnaeus 



SPONDYLUS STRIATUS, n. sp. 

 Plate 29 



Type specimen 12276, Coll. Invert. Palae., Univ. Calif., loc. 2149. 



Shell very large, nearly oval in outline; inequivalve; beak of right valve 

 small and pointed, that of the left valve apparently large and irregular. Ante- 

 rior dorsal margin nearly straight but curving below the ear to meet the even 

 curve of the base; posterior margin slightly concave near the beaks. Anterior 

 ear of the right valve about 36 millimeters long. Shell of right valve about 10 

 millimeters thick, that of the left valve being somewhat thinner, due in part to 

 a pitted condition of the surface apparently produced by a marine organism. 

 Eight valve ornamented by a large number of fine radiating ribs, which are 

 ridged longitudinally and tend to become nodose toward the base of the shell. 

 The lower (left) valve rugose, and apparently not so distinctly ribbed. Hinge 

 and interior of the shell unknown. Length of type, 115 mm.; height, 145 mm.; 

 diameter, 75 mm. 



This species resembles a Lima in outline and in the characters of 

 the upper (right) valve. 



Horizon. — Chico group, Tellina ooides zone. 



SPONDYLUS RUGOSUS, n. sp. 

 Plate 30, figure 3; plate 26, figure 3; and plate 29, figure 3 



Type specimen 12277, Coll. Invert. Palae.; specimen 12322, Coll. Invert. Palae., 

 Univ. Calif., loc. 2143. 



Shell medium size, very inequilateral, inequivalve; right valve rather fiat; 

 left valve ventricose and very rugose. Outline of left valve irregular due to its 

 nodose character. Umbone of left valve very tumid and irregular; umbone of 

 right valve small. Ear long, equaling about one-third the height of the shell. 

 Left valve ornamented by rough growth lines which are in places extended 

 into irregular, lamellar processes, giving a very rough aspect to that valve. 

 Eight valve ornamented by numerous fine radiating ribs with imbricated spaces 

 and interspaces. Hinge and pallial line unknown. Ventral margin finely crenu- 

 lated. Length of type, 72 mm.; height, 95 mm.; diameter, about 40 mm. 



The right valve of this species resembles that of the preceding 

 species in general outline and convexity, but it differs from it in having 

 imbricated instead of ridged ribs and in having a more conspicuously 

 crenulated margin. Another specimen from locality 2143 has a more 

 irregular left valve, with a portion of the right valve showing a small 

 part of the surface covered with imbricated ribs. The inner margins 

 of the left valve of that specimen are conspicuously crenulated from 

 a point near the beak to the base of the shell. 



The exact locality within Silverado Canon from which the type 

 specimen (no. 12277) was obtained is unknown. 



Horizon. — Chico group, Actaeonella oviformis zone. 



