Abstract

A geometric model is proposed to explain the quincunx pattern of punctae which characterizes most terebratuloids. This model gives the two parameters d and g, which together express the density of punctae. The pattern of punctae in dalmanelloids does not differ in its basic geometry from that of the terebratuloids and can be defined by the same parameters. This also holds for the punctate spiriferoids and the punctate orthotetid genus Streptorhynchus. The pattern of pustules in the taleolate brachiopods differs from that of the model for the quincunx pattern of punctae, but can still be expressed in terms of d and g. In this case d corresponds to the wavelength of the costellae. Both punctae and pustules are morphologically and numerically related to the marginal setae.

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