26 PROCEEDINGS OF TIIE 



passages which communicate with the columnar canal (PI. I. figs. 5, 

 7, and 9). The passages in question vary in length and form — they 

 may be short, and without any form in particular (PL I. fig. 5), or 

 they may be of some length, and distinctly funnel-shaped (PI. I. 

 fig. 7). An interesting and well-marked example lies before me, 

 from Roscobie, contained in the collection of the Geological Survey 

 of Scotland. The stem (PI. I. figs. 1, 2, and 3) is a gradually 

 enlarging one, and was cut at three different points, representing a 

 space of 1| in. vertical. The middle section passed almost through 

 the centre of the plug, and shows (PL I. fig. 3) the partially funnel- 

 shaped passage leading to the columnar canal. The latter contains 

 (PL I. figs. 2 and 3) a piece of black matrix (?) reposing against 

 its further wall, and somewhat crescentiform in appearance. Both 

 the upper (fig. 2) and lower section show the same black fragment 

 extending upwards and downwards through the canal. It will be 

 noticed that in this specimen the aperture is placed in a longitudinal 

 depression, extending some distance up and down the stem. PL II. 

 fi£>\ 6 is a section of a small stem in the British Museum Collec- 

 tion from the English Carboniferous limestone series, and shows a 

 remarkably straight and direct passage leading towards the central 

 canal, but not reaching it. The passage dilates very slightly at its 

 termination. 



In the vertical section of another specimen in the British Museum 

 Collection, an infilling of matrix marks the extent of the external 

 opening leading by a more or less contracted passage to a small inner 

 cavity filled with transparent calcite, and representing the object 

 which had once dwelt within the Crinoid stem (PL II. fig. 8). 



An attentive examination of any of the cross sections will show 

 that, up to a certain point in the existence of the Crinoid, growth 

 went on regularly and steadily; but if the outermost circular lines 

 of accretion are followed round, it will be seen that, on arriving at 

 the pocket, or passage, as the case may be, they curve inwards, 

 following the latter, whereas those nearer the centre, on reaching 

 the passage, simply abut against it. I believe the accretion lines 

 with the inwardly curved termination to be simply those which 

 were acquired by the column after the injury had been done, and 

 the size of the aperture seen on the exterior of a column depends 

 to a certain degree on the extent to which this process has gone. 

 It is, of course, also dependent upon the original size of the aperture 

 and passage. 



