150 University of California Publications in Geology [Vol. 13 



MODIOLUS VEBONENSIS, n. sp. 

 Plate 3, figure 4 

 Type.-^No. 12373, Univ. Calif. Mus. Pal. 



Shell small to medium in size, flat and elongate; anterior end extending only 

 slightly beyond beak; posterior dorsal edge straight and not separated from the 

 posterior end by any well defined angle; anterior dorsal edge slightly concave; 

 base evenly rounded; surface smooth, except for concentric lines of growth. 



Dimensions. — Type specimen U. C. no. 12373; length, 40.6 mm.; greatest width, 

 17.9 mm. 



Occurrence. — Briones formation. Type specimen from U. C. loc. no. 3529. 



Family Cyrenidae 

 Genus CYRENA Lamarck 

 CYRENA (CORBICULA) DIABLOENSIS, n. sp. 

 Piate 3, figures 5a and 5b 

 Type.— No. 1237-4, Univ. Calif. Mus. Pal. 



Shell medium in size, subcircular; beaks anterior to the middle of the shell, 

 inconspicuous, and only slightly prosogyrous; dorsal margins straight and nearly 

 equal; surface smooth except for fairly heavy, irregular lines of growth; hinge 

 plate heavy; posterior cardinal not as heavy as two anterior cardinals; nymph 

 plate fairly long for this genus, but not as wide or as prominent as is often the 

 case with Cyrena. 



Dimensions. — Type specimen U. C. no. 12374; alt., 37.6 mm.; width, 42.4 mm. 

 Occurrence. — Upper San Pablo formation, U. C. loc. no. 1949. 



This species differs from C. calif ornica Gabb, 22 found in the same 

 horizon, in being more circular in outline, in having less conspicuous 

 beaks, which are less prosogyrous, in having heavier teeth and more 

 obsolete laterals, and in possessing a less prominent nymph plate. 



Family Cardiidae 

 Genus CARDIUM Linne 

 CAEDIUM COBBIS, n. var.? 

 Plate 5, figure 3 

 Specimen.— No. 12376, Univ. Calif. Mus. Pal. 



Shell is very similar to Cardium corbis (Martyn), 2 3 but differs in having on 

 the average three or four less ribs. The Briones form has 29 to 30 ribs, while 

 the recent form (the typical C. corbis) has 33 to 34. The preservation on all the 

 specimens found in the Briones as yet is very poor, and it is difficult to tell 

 whether this is a new variety of C. corbis or not. However, the twenty-nine ribs 

 appear to be quite constant on the seven specimens at hand. 



Dimensions. — Specimen figured is U. C. no. 12376; alt., 34 mm.; width, 40 mm. 



Occurrence. — Briones formation. Specimen figured from U. C. loc. no. 207. 



Gabb, Calif. State Geol. Surv., Palaeontology of California, vol. 2, p. 26, 

 fig. 45, 1869. 



23 Martyn, Univ. Conch., pi. XXVIII, fig. 2, 1784. 



