The relative length and width of the two specimens is different, the smaller specimen not being so convex at the base as the one measured. YOLDIA. Y. COOPERII, G. Y. t. tenui, compressiuscula, valde inæquilaterali, antice angusta, postice expansa; umbonibus minutis, per positionem anteriorem excentricis; epidermide olivacea, nitida; concentrice et confertim lirata; liris minutis, sub lamellosis; intus lactea; cicatricibus muscularibus magnis. Long. 1·25, lat. 2·6, alt. ·25. Shell thin, somewhat compressed, very inequilateral, beaks placed about a third of the length from the anterior end, minute; anterior end narrow, sub-acuminate, posterior end broadly rounded; base most prominent just posterior to the middle of the shell; surface sculptured by numerous small concentric ribs, rarely dichotomous or anastomosing on the widest part of the shell; these ribs are flat and abruptly truncated on the side nearest the beak, giving the surface, under a glass, the appearance of an overlapping. Epidermis shining, olivaceous; internally a bluish white; muscular scars large, the anterior triangular, posterior a third the largest, broadly suboval. A single fresh valve was found on the beach at Santa Cruz, Cal., by Dr. Cooper. Earthquakes in California during 1864. BY DR. JOHN B. TRASK. FEB. 26TH, 0 h. 40 m.—A light shock of earthquake at San Francisco. At 5 h. 45 m. a smart shock, having three distinct vibrations. On the day previous, an “_Electric Storm_” prevailed between Visalia, Tulare Co., and Los Angeles, which was very violent in its effects on the telegraph lines. On the 27th, a heavy “Norther” commenced and continued till the eve of the 28th. This earthquake was felt at San José, fifty miles south, at the same hour, and was marked by two very smart shocks following each other in quick succession. MARCH 5TH, 8 h. 49 m.—A smart shock of earthquake at San Francisco. The earthquake began at the above hour. The first wave was in a direction north and south, and lasted one and three-fourths seconds. Nearly one and a half seconds elapsed before the second shock, which occurred at forty-nine minutes, three seconds past eight o’clock, and had a duration of one and one-half seconds. The motion in this shock was rotatory. Magnetism was _not_ suspended in this nor either of the other shocks, this year. The total length of time included in this earthquake, was nearly 5 seconds. These observations were made at the height of 20 feet 4 inches above the ground, but persons situated at a greater height felt the vibrations longer and more severely.