The appearance of this northern genus among the Mopaliæ and Ischnochitons is very remarkable; as is the character of the mantle-margin. Genus NACELLA, Schumacher. _Nacella (? palleacea, var.) triangularis_, Cpr. State Coll. No. 416_c_. N. t. “_N. palleacea_” simili, sed multo minus elongatâ; apice elato, marginibus rectangulatim divergentibus; albidâ, maculis fuscis perpaucis ornatâ; striulis subobsoletis. Long. 0·28, lat. 0·12, alt. 0·18, div. 90°. _Hab._ Monterey, 4 dredged dead, _Cooper_. Probably a distinct species. The solitary shell sent by Dr. Cooper is shaped like a right-angled triangle, with five large brown spots near the base. _? Nacella subspiralis_, Cpr.? n. s. State Collection, 416b. ? N. t. parvâ, carneâ, lævi, tenuissimâ; vertice “_Emarginulæ_” simulante, subspirali, sed apice patelloideo, adunco; t. adultâ valde elevatâ; margine laterali antico subrecto, apice projiciente, valde remoto; postico maxime fornicato; aperturæ margine antice et postice prolongato. Long. 0·26, lat. 0·19, alt. 0·20, div. 80°. _Hab._ Catalina Island, 10-20 fm., 4 dead, _Cooper_. This may be the young of the long-lost _Patella calyptra_, Mart. It may be a _Scutellina_. Even the genus cannot be predicated from the shell alone. Genus ACMÆA, Eschholtz. _Acmæa (? pileolus, var.) rosacea_, Cpr. A. t. parvâ, conicâ, tenui, lævi; t. jun. pallide rosaceâ, elegantissime maculis albis et fuscis subradiatim sparsis; t. adulta strigis fusco-rosaceis et albidis pictâ; apice elevato, parum antico; intus rosaceo. Long. 0·20, lat. 0·16, alt. 0·08, div. 100°. _Hab._ San Diego, 1 sp. jun. (_Palmer_): Monterey, 1 dead sp. _Cooper_. The absence of striæ, very thin texture, and regularly conical growth, distinguish this shell from _A. patina_, a rare variety of which has a pinkish tinge. Specimens in Mus. Cuming are marked “_pileolus_, Midd.,” but do not accord with the diagnosis. It is almost exactly like Herm[19] specimens of _A. virginea_. Col. Jewett’s similar shells, marked “Panama,” were perhaps West Indian. Genus SCURRIA (?), Gray. _Scurria (?) funiculata_, Cpr. (?) n. s. State Collection, No. 466_d_. ? Sc. t. parvâ, albidâ, regulariter conicâ, apice acuto, elevato, parum antrorsum sito; liris validis, rotundatis, interdum vix nodulosis, irregulariter, huc et illuc duplo vel tripliciter dispositis; margine à costis extus undato; cicatrice haud conspicuo. Long. 0·50, lat. 0·38, alt. 0·26, div. 80°. _Hab._ Monterey, 6 dredged dead, _Cooper_. So different from the most strongly marked young specimens of _Sc. mitra_ that I presume it to be distinct. The genus depends on the animal, which has not yet been seen. Genus PUNCTURELLA, Lowe. _Puncturella Cooperi_, Cpr. n. s. State Collection No. 1029.