This bivalve may be found burrowing in sandy mud or swimming in shallow coves and inlets. At Woods Hole, Mass., it is easily obtained by dredging in Eel Pond or Hadley Harbor; the pollution of Eel Pond, however, is not conducive to the development of prime individuals.

The sexes are separate and are easily recognized during the breeding season. The ripe gonads are very extensive and surround the visceral mass just above the foot; in mature females, they are chocolate brown in color, in males they are yellow.

Probably during the early summer months. However, the season has not been determined for the Woods Hole area.

A. Care of Adults: Adults may be kept in aquaria or in large fingerbowls supplied with running sea water.

B. Procuring Gametes: It is not known whether eggs removed from the gonads can be artificially inseminated. Mature animals, however, will spawn spontaneously in the laboratory.

C. Preparation of Cultures: Naturally-inseminated eggs may be reared through metamorphosis. No special feeding is necessary, as the larvae are well supplied with yolk. They are free-swimming and should be decanted daily to fresh sea water.

A. The Unfertilized Ovum: The mature egg measures approximately 150 microns in diameter, and is free of membranes (Drew, 1897). It is chocolate brown in color and very opaque, containing a large amount of yolk. Two polar bodies are extruded and lost shortly after the ovum is shed.

B. Cleavage: Cleavage is total, unequal and spiral. Gastrulation is by epiboly.

C. Rate of Development: Development is fairly rapid. The first cleavage occurs about two hours after insemination. By 36 hours, the swimming embryo has a developing shell gland and cerebral ganglion, and by 80 to 105 hours it metamorphoses.

D. Later Stages of Development and Metamorphosis: The early barrel-shaped larva is marked by a unique structure: a ciliated outer covering which is discarded at metamorphosis. The ectodermal cells which form this covering, or test, are arranged in five distinct rows. The two end rows are covered with short, evenly distributed cilia, and each of the intervening rows bears a band of longer, powerful cilia. A very long apical tuft is visible at one pole, and at the opposite pole is the blastopore. Close to this, on one side, there is a small invagination, the stomodeum. Beneath the test, another ectodermal layer is formed, that of the embryo proper.

At metamorphosis, the animals settle to the bottom, the apical cilia shrivel, and the test cells disintegrate. The young animal which emerges has a pair of straight hinged shell valves, otocysts containing otoliths, and a well-developed foot which becomes active within a few hours. There are rudimentary gills and a complex rudimentary digestive tract. Further details, and illustrations of the development of this animal, may be found in the papers by Drew (1897, 1899a, 1899b).).

DREW, G. A., 1897. Notes on the embryology, anatomy, and habits of Yoldia limatula, Say. Johns Hopkins Univ. Circ., 17: 11-14.

DREW, G. A., 1899a. The anatomy, habits, and embryology of Yoldia limatula, Say. Mem. Biol. Lab., Johns Hopkins Univ., 4: no. 3, 1-37.

DREW, G. A., 1899b. Some observations on the habits, anatomy and embryology of members of the Protobranchia. Anat. Anz., 15: 493-519.