Contrasting modes of construction of Retiolite - type Rhabdosomes

Abstract

1. In a morphological series including Reteograptus geinitzianus, Gothograptus nassa, Holoretiolites spp. and 'Retiolies' sp. it is possible to demonstrate that sclerotization of the periderm secreted between the zooid and its mantle evagination became progressively localized, culminating in the formation of the highly specialized and sparse framework of Holoretiolites and 'Retiolites' sp. 2. In Retiolites geinitzianus (Barrande) the same kind of peridermal secretion combined with localized sclerotization to produce a superficially similar type of rhabdosome to some of those in the above morphological series, but with a quite different relationship to the secretary tissues of the zooids.