1922] Trash: The Briones Formation of Middle California 157 



Note. — In the specimens found in the Briones formation the varices 

 are not so pronounced as those from the Lower San Pablo ; but the 

 Briones forms appear to be somewhat eroded, and since they are 

 similar to the Lower San Pablo forms in other respects, they are 

 ascribed to the Lower San Pablo species. 



Family Thaisidae 

 Genus ACANTHINA Fischer de Waldheim 

 ACANTITINA PERRINI, n. sp. 

 Plate 8, figures la and lb 

 Type in Stanford University Paleontological Collection. 



Shell small to medium in size; whorls four; body whorl about two-thirds the 

 height of the shell; sutures appressed; whorls with a prominent angulation, 

 which on the body whorl is a little above the middle; on the whorls of spire 

 angulation comes just above the suture; surface posterior to angulation slopes 

 upward at an angle of about 45°; whorls with about eleven nodes on line of 

 angulation, which are more prominent on the posterior whorls of the spire, 

 where the nodes might be classed as longitudinal ribs; these nodes tend to 

 become obsolete upon the body whorl; surface smooth except where lines of 

 growth form depression on lower part of shell, which is characteristic of this 

 genus; canal short, recurved; inner lip smooth; outer lip not preserved. 



Dimensions. — Type specimen alt., 32.5 mm.; max. width, 26.3 mm.; alt. of 

 aperture, 21.3 mm. 



Occurrence. — Briones formation?. About six miles south of Livermore. Type 

 in Stanford University collection. 



Named in honor of Professor James Perrin Smith, Stanford University. 



This species is quite distinct because of its low spire and broad 

 body whorl. 



Genus KOILOPLEURA, n. gen. 

 Plate 8, figures 2, 3a, 3b, 4a, and 4b 



Type.—^o. 11900; Cotype.— No. 12393, Univ. Calif. Mus. Pal. 



Shell solid, elongate, medium spire; sutures deeply impressed, bordered by 

 a raised tabulation; lower part of body whorl with prominent angulation, 

 below which the shell rapidly narrows to form the canal; surface of shell 

 between angulations markedly concave; outer lip with spine, causing pronounced 

 narrow depression on lower part of body whorl below lower angulation; canal 

 moderately long, rather wide, very deep, and curved posteriorly; umbilicus 

 pronounced and subperforate. 



Dimensions. — Genotype specimen U. C. no. 11900; alt., 35 mm.; greatest width, 

 20 mm.; alt. of aperture, 27 mm. Cotype, U. C. no. 12393; alt., 49 mm.; greatest 

 width, 24 mm.; alt. of aperture, 27 mm. 



Occurrence. — Briones formation (Upper Miocene). Type from U. C. loc. 

 no. 1354; cotype from loc. no. 1455. 



