124 poterioceinidil', fentacrinus. 



Formation and Localities. 

 London Clay, near White Conduit House, Islington ; Richmond, and Kensington. 



7. Species. Pentacrinus Prattii. (Austin,) 



Plate 16, Fi(/. 4 a, to 4 c. 



This is another instance of a species founded on the evidence of the column alone, 

 a practice which is highly objectionable when the disjointed remains of diflTcrent crinoids 

 are found in profusion scattered through the same matrix, but which is perfectly safe 

 when only the column occurs in a particular group of rocks, for it has now become 

 almost certain that each formation has its characteristic crinoids, as it has its distinctive 

 mollusca, and other organic bodies. 



Formation and Locality. 



The Tertiary beds at Bieritz, in the vicinity of Bayonne. 



The column is massive, the joints of which are generally uniform in thickness, and 

 the angles rounded in a similar manner to the E.vtracrinus lepklotus, but considerably 

 more so than even in tliat crinoid, which was long considered as the least angular of all 

 the floriform pentagonal columns. The spaces betweeen the crenated ridges on the 

 articulating facets of the jomts are deeply impressed, so that the tranverse fibrous 

 cushions wiiich were interposed between the articulations, added by their contractile 

 power to the flexure of the column. 



We know but little of the history of this species beyond the fact that Mr- Pratt 

 brought several specimens of columns from the tertiary beds in the vicinity of Bayonne, 

 but we are not aware that any other portion of the animal has been discovered, either 

 detached from, or in connection with the column, nor do we know of even a single 

 instance in which the body of a crinoid has been discovered in the Tertiary Rocks of 

 this country, or of any other part of the globe. 



