The life history of the porcellanid crab Petrolisthes lamarckii (Leach) has been worked out, thus extending the knowledge of the larvae of the genus to six species. In P. lamarckii two zoeal and a megalopa stages along with first crab-instar have been observed in the laboratory. These stages have been fully described and illustrated. Average number of days spent in each stage has been also given.

The validity of telson characters as of generic significance is discussed in the light of larval evidence in the six species described so far and in the other Porcellanid genus Pachycheles. Also a key to the first zoeal stage of the known species of the genus Petrolisthes is given