C. t. “_C. biradiatæ_,” formâ simulante, sed multo minore; haud obesâ, transversâ, luteo-cinereâ, dorsum versum interdum obscure biradiatâ; angulo plus minusve carinato, postice definito; antice rotundatâ, expansâ; concentrice crebre sed obtuse lirulatâ; umbonibus obtusis; intus, dentibus minoribus; linea pallii angulatâ, haud sinuatâ; cicatricibus adductoribus callosis; margine t. adultâ postice altero alterum amplectante. Long. 0·42, lat. 0·28, alt. 0·16. _Hab._ San Diego, San Pedro, 50, alive, at low water. Genus PLECTODON.[16] Cpr. Testa tenuis, scaber, rostrata, haud inflata: margo dorsalis sub umbones intus nexa, dentem cardinalem formans: dentes laterales longi, laminati: cartilago fossâ minutâ, sub umbones celatâ, dente laterali postico contiguâ, sita: sinus pallii parvus. _Plectodon scaber_, Cpr. n. s. State Collection, No. 1062. Pl. t. _ledæ_-formi, tenui, subdiaphanâ, pallidâ; totâ superficie minute pustulosâ; marginibus dorsalibus rectis, ad angulum 150°; antice et ventraliter productâ, marginibus excurvatis; postice valde rostratâ, truncatâ: intus, margine sub umbones interrupto; plicâ ex apice oblique usque ad marginem dorsalem anticum excurrente; dentibus lateralibus laminatis, extantibus, postico longiore; cicatricibus adductoribus parvis, subrotundatis, ad extremitates dentium lateralium sitis; sinu palii lato, haud impresso. Long. 0·62, lat. 0·34, alt. 0·20. _Hab._ Catalina Island, two right valves, 40-60 fms, Cp. This very distinct genus has the aspect of Theora, and appears allied to Neæra. It is probable that the cartilage was strengthened by an ossicle. The great peculiarity is the twisting-in of the dorsal margin, which ascends the umbo in a very loose spiral. Genus MACOMA, Leach. _Macoma indentata_, Cpr. n. s. State Collection, No. 365. M. t. “M. sectæ” simili; sed postice valde rostratâ, sinu inter plicam et regionem ventralem valde expansam indentato. Long. 2·20, lat. 1·40, alt. 0·56. _Hab._ San Pedro, (young, living, _Palmer_;) large dead valves, _Cooper_. Differs from _M. umbonella_, Lam., in its _secta_-like post-ligamental wing. This being rubbed off in the large dead valves, the shell has the aspect of a very distinct species. GENUS ŒDALINA, CPR. _Œdalia_, Cpr., Brit. Ass. Rep., 1864. (pre-occup.) Subgenus COOPERELLA, Cpr. _Œdalina_; cartilagine fossâ semi-internâ, ligamento externo contiguâ, sitâ; dentibus cardinalibus laminatis, haud bifidis, sen uno bifido. Dedicated to the memory of Judge Cooper, of Hoboken, N.J., author of the Report on the Mollusca of the Pacific Railway Expeditions. _Cooperella scintillæformis_, Cpr. n. sp. State Collection, No. 533 a.