P. t. oblongâ, parvâ, subquadratâ, valde inæquilaterali; parte anticâ fere nullâ; marginibus, dorsalibus subrectis, fere rectangulatis, ventrali parum excurvato, postico rotundato; umbonibus antice flectis; lunulâ parvâ, concavâ: intus, v. sinistr., dent. lat. post. per totam longitudinem dorsalem decurrente, parte cardinali acutâ, alte transversim sulcatâ; ant. secundum lunulam incurvato curto, serrato; cicatr. adduct. sub fines dentium sitis. Long. 0·14, lat. 0·10, alt. 0·06. _Hab._ San Diego; 1 worn valve among shell washings. _Cooper_. Genus LEDA, Schumacher. _Leda hamata_, Cpr. n. s. State Collection, No. 984. L. t. “_L. caudatæ_” simili, sed valde hamatâ; planatâ, valde inæquilaterali; umbonibus angustioribus, lævibus, ad trientem sitis; marginibus, dors. post. maxime incurvato, ant. parum, ventr. valde excurvatis; parte posticâ valde rostratâ, rostro biangulato, curvato, angustiore, biangulatâ; sulcis et costis validis, concentricis, supra rostrum continuis, dorsum versus postice obsoletis. Long. 0·37, lat. 0·10, alt. 0·10. Genus ACANTHOCHITES, Risso? (Leach, 1826). _Acanthochites avicula_, Cpr. n. s. State Collection, No. 1072. A. t. “_A. arragonitei_” formâ magnitudine, pallio, et indole simillimâ; sed sculpturâ et laminis terminalibus diversâ; jugo longitudinaliter sulculis circ. vi. instructis, interstitiis quasi planato-squamosis, umbonibus latis; areis diagonalibus haud definitis; lateribus, squamis (quoad magnitudinem) maximis, planatis, ovalibus ornatis, seriebus indistinctis divergentibus instructis; mucrone parvo, antice sito; colore livido et olivaceo-fusco varie tincto; laminis insertionis valv. lat. ut in _A. arragonite_; anticâ, fissuris v. Long. 0·16, lat. 0·10. _Hab._ Catalina Island, 10-20 fm., rare; _Cooper_. Genus ACANTHOPLEURA, Guilding. _Acanthopleura fluxa_, _Cpr._? n. s. A. t. “_A. scabræ_” simili, sed latiore, pallidiore; viridi, rubro-aurantio conspersâ; valvis rectangulatis; suturis marginalibus haud conspicuis; areis diagonalibus satis distinctis; radiis obtusis fluxis ii., alterâ diagonali, alterâ suturali; totâ superficie conspicue granulosâ, granulis acutioribus præsertim albidis; jugo obtuso, vix vallato: laminis insertionis ut in A. scabrâ instructis. Long. 0·60, lat. 0·40, div. 110°. _Hab._ Santa Barbara Island, _Cooper_. Foot, in the only dried specimen seen, extremely thin, flat, and narrow. Genus ISCHNOCHITON, Gray. _Ischnochiton veredentiens_, Cpr. n. s. State Collection, No. 518 _a_ (bis).