NO, 2116. ANATINACEA FROM WEST COAST OF AMERICA— BALL. 445 

 CYATHODONTA DUBIOSA, new species. 



Shell in general resembling C. undulata on a smaller scale. The 

 left valve is nearly as convex as the right valve. The plaits are less 

 regular, becoming obsolete behuid and toward the basal margin. 

 The left valve has only two very faint rays, the right valve also two, 

 of which the dorsal one is strong. The granulation is in somewhat 

 irregular concentric lines and not radially distributed; the pallial 

 sinus is not so high relatively and falls short of reaching the vertical 

 of the beaks. Length, 38; height, 29; diameter of right valve, 9; 

 of left valve, 7.2; vertical, 15 mm. in front of the posterior end. 



Distribution. — San Pedro to San Diego, California, and to La Paz, 

 Lower California. Cat. No. 96450, U.S.N.M. Type locaHty, off 

 La Paz. 



The most obvious distinction between this and C. undulata of the 

 same size lies in the greater relative convexity of the left valve in 

 C. duhiosa. 



CYATHODONTA LUCASANA, new species. 



Shell small, whitish, translucent, fragile, elongate-quadrate, the 

 anterior end longer; hinge marginal, feeble, a half -ring-shaped hth- 

 odesma in front of the resUifer; posterior end trimcate, with a 

 rounded ridge from the umbo to the basal end of the truncation; pli- 

 cations few and sparse; no granulation perceptible, and the sinus 

 invisible on account of the translucency of the shell. Length, 7.5; 

 height, 5; diameter, 3.75; vertical, 3 mm. in front of the posterior 

 end. 



Distribution, — ^Type locality, Cape St. Lucas, Lower California, 

 Xantus. Cat. No. 159106, U.S.N.M. 



Not identical with the young of any of the other species. 



CYATHODONTA PEDROANA, new species. 



Shell small, white, resembhng C. dubiosa but more pointed behind, 

 hardly truncate, anterior end longer; valves nearly equally convex; 

 the plaits are more numerous (±25), narrower, more close-set, and 

 more regular, they reach the posterior dorsal margin; the rays are 

 obscure; the granulations obscurely concentrically disposed; the 

 sinus is small, shallow, and does not reach the vertical of the beaks. 

 Length, 27; posterior end to vertical, 10; height, 21; diameter of 

 right valve, 6; of left valve, 5 mm. 



Distribution. — Type locahty, in mud dredged from the channel of 

 San Pedro Harbor, CaUfornia. Also at Catahna Island. Cat. No. 

 207527, U.S.N.M. 



This was quite abundant in the mud excavated by the Government 

 dredgers, and is a particularly neat, compact, and pretty species. 



