418 University of California Publications in Geology [Vol. 13 



Trigonarca Conrad 

 TEIGONARCA CALIFORNICA, n. sp. 

 Plate 25, figures 2a and 2b 



Type specimen 12313, Coll. Invert. Palae., Univ. Calif., loc. 2141. 



Shell trigonal in outline, inequilateral, the posterior end being greatly pro- 

 duced; separated by a wide dorsal area; anterior end short, rather bluntly 

 rounded; posterior end pointed; base line nearly straight, oblique to the hinge 

 line. Umbones small, beaks acutely pointed; umbonal ridge extends from the 

 beak to the posterior extremity. Area between umbonal ridge and posterior 

 margin of shell flattened, and strongly depressed. Dorsal area deeply exca- 

 vated, marked by at least five deeply incised chevron lines. Surface of shell 

 sculptured by irregular lines of growth. Dentition consists of ten short, straight, 

 posterior teeth, placed obliquely upon the hinge plate, and a less number of 

 short, heavy, anterior teeth. Length, 52 mm.; height, 35 mm.; convexity, 15 mm. 



In general form this species recalls Cucullaea decurtata Gabb, from 

 which it differs in its less ventricose shape, more elongated posterior 

 end, and its more pronounced umbonal ridge. 



Horizon. — Chico group, Actaeonella oviformis zone. 



TEIGONARCA EXCAVATA, n. sp. 

 Plate 25, figures la and 15 



Type specimen 12315, Coll. Invert. Palae., Univ. Calif., loc. 2141. 



Shell large, elongate, inequilateral; posterior margin extends nearly straight 

 from the hinge to the pointed posterior extremity. Beaks small, widely separ- 

 ated, situated about one-third the distance from the anterior to the posterior 

 end; anterior margin produced, evenly rounded from the anterior end of the 

 hinge line to the base. A pronounced umbonal ridge extends from beak to the 

 posterior end. Ventral margin nearly straight and not parallel to the hinge line. 

 Posterior dorsal area broad and excavated. Surface of the shell smooth except 

 for a few incremental lines of growth. The hinge of the right valve with three 

 heavy, straight, anterior teeth situated obliquely upon the hinge plate; posterior 

 teeth, four in number, separated from anterior by sixteen small, nodular teeth 

 perpendicular to hinge line. Length of type, 62+ mm.; height, 40 mm.; con- 

 vexity, 25 mm. 



This species resembles T. brahminica Forbes from the Arrialoor 

 group of India, but it differs from that species in the absence of radial 

 sculpture. Its more ventricose shape, longer anterior extremity, and 

 its relatively larger teeth distinguish this species from T. calif ornica. 



Horizon. — Chico group, Actaeonella oviformis zone. 



