On additional embryonic forms of trilobites from the Primordial rocks of Troy, New York, with observations on the genera Olenellus, Paradoxides, and Hydrocephalus.

AMONG the various species of rrrilobites of the genus P(ll'adoxides (abstracting those forms of which we know the tllOnicic Htructure but imperfectly or not at all), there may be distinguished two principal groups: One characterized by havi ng