41
1
January
173
182
RUTA, M. 1998. An abnormal specimen of the Silurian anomalocystitid mitrate Placocystites forbesianus. Palaeontology, 41, 1, 173–182.
Marcello Ruta An unusual specimen of the Silurian anomalocystitid mitrate Placocyxiites forbesianus K described. Unlike the normal morphology of the species, the anterior, transverse row of ventral plates consists of two rather than three elements; the mid-ventral plate of the next posterior transverse row is reduced in size and wedged between the lateral elements of the same row; the plate arrangement on the anterior half of the ventral skeleton is asymmetrical; the left lateral and admedian ventral plates are smaller than the corresponding plates of the right side; finally, the placocystid plate has a slightly pronounced anterior angle. The abnormal skeletal features of this specimen are interpreted as a developmental response to the absence of an anterior ventral plate. The Palaeontological Association (Free Access)