ABSTRACT
Passalocrinus, originally described as a Lower Carboniferous niicrocrinoid, is ajuvenile blastoid. The theca, commonly less than 1mm high, is a closed capsule that consists of 3 basal plates, 5 unequal radiais and 5 orals. Identification of Passalocrinus as juvenile blastoids is based on : 1) Epidemiological evidence that Passalocrinus occur in samples containing blastoids from Silurian to Permian; 2) that where a blastoid has the azygous basal in an atypical position, so too does the accompanying Passalocrinus’, 3) the presence in large specimens oí Passalocrinus of growth lirae similar to those of adult blastoids; 4) the reconstruction of the early ontogeny of small blastoids from growth lirae close to the distal surfaces of radiais, which demonstrates that during the earliest part of the growth history, the radiais had the characteristic shape of those of Passalocrinus.
