39.2 Dr. F. A. Bather on British Fossil Cricoids : 



111 pentajjonal forms therefore the cracks coincide with the 

 angles. This indicates tliat the weak stereom occupies the 

 liganieutar tracts, as luiglit be expected. Further evidence 

 of tliis is afforded by the five interradial pillars of dark 

 colour that ruu through every interuode from top to bottom 

 and are seen on broken or ground surfaces (e. ff., E 22024), 

 for the colour is due to the carbouized remains of the 

 ligaments (see Bather. 1893, ' Crin. Gotland/ p. 151, and 

 1909, 'Trias. Echin. Bakouy/ p. 204). 



In mean Diameter the fragments varv from 4 mm. 

 (E 21953) to 9-4 (E 22027). This doubtless represents 

 growth^ and the larger forms are by far the more common 

 in the collection. 



The Side-Faces in a large number of specimens are quite 

 smooth, but in some there are small granules scattered over 

 the surface (E 21966) ; these granules may be elongate 

 either vertically or transversely, and may run together to 

 form irregular lines, a sort of vermiculation (E 21965) ; or 

 they may run into transverse ridges, at the equator and the 

 sutural margins (E 22024) ; the commonest arrangement 

 seems to be one ridge at the equator of the columnal, either 

 compound (E 21968) or simple (E 21969, cf. d'Archiac's 

 fig. 17«),and this is often accompanied by an equatorial 

 swelling of the columnal (E 22022). In such cases the 

 intervening granules, if any, tend to lie beside each radius 

 (E 22020 and E 22023). 



This leads to another series of variations, namely from a 

 plane side-face, producing a straight-sided column (E 22021), 

 through slightly swollen, to obtusely ridged (E 21970 to 

 E 21974). The ridge is often sharply cut and may be 

 smooth, or accentuated by the line of granules previously 

 mentioned. In one specimen, E 21985, the side-faces are 

 slightly excavate, or, in other words, the columnal is thickened 

 at the sutures. 



In the smooth specimens the columnals are equal in 

 height (cf. d'Archiac's fig. 18), except for the slightly higher 

 epizygal and slightly lower hypozygal. The following are a 

 few measurements : — 



Inequality*in height of columnals usually becomes manifest 



