Abstract

"The ontogeny of Dalmanitina olini Temple (upper Ordovician) is described on the basis of specimens from Scania [southern Sweden] and north Wales. The development is similar to that of D. socialis (Barrande), but good preservation has enabled some detailed changes in the cephalon to be followed. The protaspid and early post-protaspid stages bear an anterior pit in each axial furrow opposite the frontal lobe. The protaspid anterior glabellar furrow becomes joined to this pit by an oblique furrow, and forms with the latter a composite oblique furrow which develops into the adult anterior glabellar furrow. This mode of development is considered probably to be common to all phacopids; the significance of the anterior pits in this family is discussed. Preliminary observations are made on the growth-rates of various parts of the glabella, and the frontal lobe is found to grow in length (sag.) at a rate approximately equal to that of the rest of the glabella."

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