POTEEIOCEINIDiE.— POTERIOCRINUS. gl 



Synonymes and References. 



Poteriocrinus quinquangularis. — Messrs. Austin, Ann. and Mag. Nat. Hist. Vol. 10, 



p. 108, Vol. 11, p. 196. 



Formation and Localities. 



Mountain Limestone. — Blacii Rock, Avon Side, Bristol ; Hook Point, Wexford ; 

 Clevedon Bay. 



A group of this small species of Poteriocrinus, was discovered by the Authors, a few 

 years since in the mountain limestone of Ireland. At a subsequent period they found 

 it in the same formation in the vicinity of Bristol. It is a small neat species with a 

 remarkably elegant column, which is quinquangular in its upper part, and circular 

 towards the base, and composed of small thin joints, alternating with larger and thicker 

 ones. Auxiliary side arms occur at certain intervals on the lower part of the column, 

 where it becomes less pentagonal than at the summit. These side arms emanate from 

 between the angles of the larger joints, never on the angles themselves. Sometimes 

 there is a minute tubercle on each of the angles of the columnar joints, which adds 

 considerably to the beauty of the column. 



The body is slender and much attenuated at its attachment to the column. The 

 proboscis is large and centrical, the mouth being situated at the apex. The surface of 

 the oral tube is striated transversely in bands, the striae of one band of plates uniting 

 at the sutures, with those on the adjoining plates. 



The divisional rays appear to amount to ten, the first and only apparent bifurcations 

 occurring at about the fifth articulation from the ray bearing plates. These plates are 

 excavated in their centres for the attachment of the rays, which are slender as compared 

 with most otjier species of Poteriocrinus. 



