Tagelus plebeius were spawned and their larvae reared in the laboratory. Length measured from 90 to 170 μ, height from 75 to 161 μ and depth from 45 to 131 μ during pelagic stages. The hinge line was 63 to 75 μ long. Larvae had a distinctive series of irregular teeth at both ends of the hinge line. They can be distinguished from other bivalve larvae by the hinge, the relatively great height of the umbo and shoulders, the much longer anterior shoulder and end, and a dark shell margin. Larvae complete pelagic development at a smaller size than any other known bivalve veliger (155–170 μ).