72 POTERIOCRINIDJ!. — POTERIOCRINUS. 



Miller represents the columnar canal as circular, wliile Professor Pliillips on the 

 contrary represents it to be pentagonal. This difference of opinion calls to mind the 

 dispute between the two travellers as to the real color of the chameleon, wherein both 

 were right, and botli were wrong. Our explanation of tlie matter as now given will 

 not, we liope, " make confusion worse confounded." 



The striae; on the facets of the columnar joints do not all radiate from the centre of the 

 column, as if they did, those at the central axis would be too much crowded ; therefore 

 to prevent this defect, which would destroy the proper adhesion of the joints, the striae 

 converging from the centre become rather wide apart at the margin. The marginal spaces 

 thus left are occupied by short striie arranged in such a manner as to make the longer 

 striae appear forked. 



Miller was the first to observe the injuries which the columns of this species so 

 frequently suflered. The effects of most of these mishaps as presented to our notice, 

 is a gradual swelling out into an unsightly protuberance of several consecutive joints, with 

 a considerable concavity on one side. This concavity has evidently been produced by 

 the violent extraction or severance of an auxiliary side arm from the column ; and the 

 crinoid in its endeavours to repair the injury and strengthen the wounded part, has by 

 a rapid and more profuse secretion of calcareous matter enlarged the joints, above and 

 below the severed member, and at the same time closed in the orifice which communi- 

 cated with the columnar canal. 



The AuxiLARY Side Arms. — These jointed appendages occur at intervals around 

 the lower portion of the column as in others of the genus. 



The columnar articulations being thin, each side arm requires several consecutive joints 

 to form a sufficient surface for its attachment. 



The base of attachment though unknown, was probably that most usually observed, 

 namely an irregular shaped mass of calcareous matter, deposited around the base 

 of the column, and on the rock to which it was attached with several root like processes 

 whii:h imparted greater stability to the tall column. 



The P. Crassus is the largest crinoid known of the genus, among which considerable 

 irregularities occur. Sometimes the rays are attached by strong ridges the whole width 

 of the ray bearing plates to the body, at others the ray bearing plates are partially exca- 

 vated to receive the basal ray joint, and few large specimens are found without traces of 

 mutilations or injuries of various kinds. 



On considering the causes which could produce such frequent bereavement of members 

 among the Poleriocrini, we are naturally led to seek for the solution of the question by 



