Nauplii of the first two stages were obtained from adult Elminius modestus and larvae of all stages, except the smallest, were obtained from the plankton over Essex oyster beds.Over 200 nauplii of all sizes were measured. Their size distribution, plotted graphically, showed six peaks corresponding to six naupliar stages. The later stages were much more variable in size than the earlier stages.The size limits and characteristics of each naupliar stage are given. Briefly, Stage I has the fronto-lateral horns pointing backwards. Stage II has the caudal spine much longer than the abdominal process. Stage III has the abdominal process about as long as the caudal spine, but has no carapace fold posteriorly. Stage IV has a carapace fold but no sign of the abdominal appendages. Stage V has the rudiments of these appendages showing indistinctly within the abdomen. In Stage VI the abdominal appendages are prominent.

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