176 CALIFORNIA ACADEMY OF SCIENCES. 



127. Mactra (Spisula) catilliformis Conrad. 



Plate XIX, Fig. 5. 



Shell large, subtrigonal, slightly ventrico.se, rather thin; umbones slightly anterior to center, 

 marginal, not prominent; a long, rather narrow, hollowed submarginal space in front of umbo; 

 anterior dorsal margin straight; anterior extremity evenly rounded near middle of shell; posterior 

 margin sharp, nearly straight; posterior extremity more obtusely rounded than anterior; ventral 

 margin prominently and evenly arcuate; surface sculptured with fine incremental lines; posterior 

 submarginal fold very faint; cartilage-pit large, triangular, very prominent; cardinal teeth not 

 prominent; laterals narrow, short; anterior ligamental area not separated from cartilage-pit; pallial 

 sinus horizontal, rather broad and shallow. 



Dimensions. — Long. 125 mm.; alt. 98 mm.; diam. 54 mm.; umbo to anterior extremity 

 50 mm.; to posterior extremity 75 mm. 



Distinguishable by its large size, broad, almost oval outline, prominent 

 cartilage pit, long, depressed area in front of umbo, and nearly equally rounded ends. 

 Siiecimen identified by Dr. Dull. 



Rather common in the upper San Pedro series at San Pedro, Los Cerritos, 

 Crawfish George's, and Deadraan Lsland. Found also in the Pliocene at Pacific 

 Beach, and in the Pleistocene at Pacific Beach, Spanish Bight and Twenty-sixth 

 Street, San Diego; and in the Pleistocene at Barlow's ranch, Ventura. The 

 specimen figured is from the upper San Pedro series at San Pedro, and is now in the 

 collection of Delos Arnold. 



Living. — West Coast. 



Pleistocene. — San Pedro; San Diego; Ventura (Arnold). 



Pliocene. — San Diego (Arnold). 



128. Mactra (Spisula) falcata Gould. 



PL.ATK XIX, Fig. 1. 



Mactra falcata Gld., Proc. Bost. Soc. Nat. Hist., Vol. Ill, 1S50, p. 216; Wilkes' Expl. Exped., 



Vol. XII, p. 393, fig. 506, 1852. 

 Standella falcata Gld., Carpenter, Brit. Assn. Rept. 1863, p. 640. Gabb, Pal. Cal., \'oI. II, 



p. 92, 1869. ^5". nasuta Gld. {fide Cooper, 7th Ann. Rept. Cal. St. Min., 1888, 



p. 266). Keep, West Coast Shells, p. 188, 1892. 

 Mactra planulata vat. falcata Gld., Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 187. 



Shell of medium size, transversely ovate-triangular, convex, rather thin; umbones about 

 central, elevated; anterior dorsal margin nearly straight; anterior extremity rounded near base; 

 ventral margin subarcuate; posterior dorsal margin slightly arcuate, and in left valve lorming a 

 slight angle behind umbo; posterior extremity not quite as sharply rounded as anterior extremity; 

 submarginal posterior ridge rounded, not prominent; hinge as in catilliformis, except cartilage-pit 

 less prominent; pallial sinus rather long, with rounded extremity, horizontal; two broad, flat ridges 

 radiate from umbo on interior surface, forming a long, triangular depression between them. 



Dimensions. — Long. 41 mm.; alt. 28 mm.; diam. 15 mm. 



Distinguishable from other species by narrower, more acutely rounded ante- 

 rior end, and interior radiating ridges. Resembles J/, californicu, but is distinguishable 



