352 John Rofe — On the Swellings on Crinoidal Columns. 



divisions of the ossicula of the column are carried round the intruder, 

 and shew on the outside as at h, fig. 1. 



The specimen ^^. 1 is evidently a section of one of these enlarge- 



ments hroken across, from which the coral has been removed, 

 probably at the time of fracture. In my collection there is nearly 

 half the circle of a Jania which has thus been removed from a 

 column to which it does not shew any appearance of having been 

 attached further than by close contact. Fig. 1 c.c. indicate moulds 

 left in the enlarged column from the coral having been removed. 



Fig. 2 is a small fragment of a column with the Jania surrounding 

 it, but not enclosed with shelly matter. Specimens in this state are 

 very rare, and probably may be accounted for by the death of the 

 Crinoid occurring before the enlargement of the column was made. 

 a.a. shew the calices of the coral. 



Fig. 3 is from a section cut across an enlargement of the column 

 where the coral is surrounded by the Crinoidal matter. It may be 

 here seen, as above stated, that the coral has attached itself to the 

 column, and by gemmation eventually surrounded it ; after which 

 the Zoophyte, whilst increasing the size of its column, has enclosed 

 the coral by a sort of exogenous secretion of shelly matter, as indi- 

 cated in the section at 6.&. ; a.a. being the calices of the coral which 

 apparently were left open whilst the coral lived, but in some speci- 

 mens they are entirely closed in. This specimen also illustrates 

 what is above stated in respect to fig. 1, for it will at once be 

 observed, that if the coral is removed there would remain the small 

 central column in the middle of the larger one, as in that figure. 



To satisfy myself that this 

 process of growth is common 

 to other Crinoidea and in other 

 geological formations, I have 

 had a similar enlargement in 

 the column of an Aj)iocrin.ite, 

 from the Bradford Clay, cut 

 both vertically and transver- 

 sely, and find that here also 

 the enlargement is due to the 

 envelopment of some foreign 

 substance attached to the 

 column, by a deposition of fresh shelly matter over and around it. 



