1922] Trash: The Briones Formation of Middle California 153 



Class GASTROPODA 

 Family Trociiidae 

 Genus CALLIOSTOMA Swainson 



CALLIOSTOMA OBLIQUISTBIATA, n. sp. 

 Plate 7, figures la and 16 

 Type.— No. 12385, Univ. Calif. Mus. Pal. 



Shell small, subcorneal; apex low; body whorl more than half height of shell; 

 sutures depressed; sides of whorls convex; body whorl with about ten oblique 

 ribs which are rounded and somewhat indistinctly nodose; ribs inclined at an 

 angle of about 30° to the revolving lines; between base and the oblique nodes 

 are two spiral ribs, the upper of which is the more prominent; lower spiral rib 

 almost at base of whorl; surface also sculptured with numerous fine oblique 

 riblets, inclined at an angle of 45° to the whorls; these are more pronounced 

 between upper spiral rib and suture; base of body whorl flat, at right angles 

 to the sides, and is ornamented with three revolving ribs; aperture not preserved. 



Dimensions. — Type specimen U. C. no. 12385; alt., 6.6 mm.; greatest width, 

 10.2 mm. 



Occurrence. — Briones formation, U. C. loc. no. 3575. 



This species resembles C. bicarinatum Clark, 26 occurring in the 

 Upper San Pablo, but it differs from the latter in that it possesses the 

 prominent oblique striations on the sides of the whorls, a lower spire, 

 less prominent nodes upon the upper part of the whorls, and it has three; 

 instead of four revolving ribs upon the base of the body whorl. 



Family Naticidae 

 Genus SINUM Bolten 

 SINUM (SIGARETUS) TRIGENARIUM, n. sp. 

 Plate 7, figures 2a and 2b 

 Type.— No. 12386, Univ. Calif. Mus. Pal. 



Shell medium in size; spire low; number of whorls to spire three; body 

 whorl large and sculptured with about thirty revolving ribs, about one to the 

 millimeter; aperture subovate, elongate posteriorly. 



Dimensions. — Type specimen U. C. no. 12386; alt., 33.5 mm.; greatest width, 

 35.3 mm.; alt. of aperture, 29 mm.; maximum width of aperture, 17.8 mm. 



Occurrence. — Briones formation, U. C. loc. no. 3576. 



This species is similar to 8. scopidosum (Conrad), 27 but it differs 

 from the latter in that it possesses thirty spiral ribs on the body whorl, 



26 Clark, Univ. Calif. Publ. Bull. Dept. Geol., vol. 8, p. 481, pi. 65, figs. 14 and 

 19, 1915. 



27 Conrad, U. S. Expl. Exp. Geol., Appendix, p. 727, pi. 19, figs. 6 and 6a, 1849. 



