YTII. Cyathocrimis. 217 



Average measurements, deduced from six specimens, with 

 allowance for variation within the limits of an individual : — 

 Height ^'5 millim. ; width below, 3*7 raillim. ; width above, 

 4*8 inilliui. Extreme measurements noted are, in ;j7i]r);') and 

 E GOO.'i respectively : — Height 2 inillim. and 6 millim. ; 

 wiiltli below, 2*o millim. and A'26 millim. ; width above, 3 

 millim, and 6*8 millim. In E 14")(), which is a medium- 

 sized specimen, the height varies from 2 b millim. in r. ant. 

 1 Vt to ^•2 millim. in 1. post., 1. ant., and ant. I JiB. 



BB 5, hexagonal ; post.B heptagonal. Average measure- 

 ments, deduced as above : — Height 6"4 millim. ; width below, 

 5'8 millim., width above, 6'7 millim. Extreme measure- 

 ments, as above : — Height 3'25 millim. and 10 millim. ; width 

 below, 3'5 millim. and 8 millim.; width above, 4'2 millim. 

 and 9'5 millim. These measurements do not take the poste- 

 rior basal into account : that is always a little larger every 

 way than the others ; thus, in E 1450, the measurements of 

 the post.B and of the other BB are as follows: — Height 6 

 millim. and 5"5 millim. ; width below, 5'75 millim. and 5"4 

 millim.; width above, 7 millim. and 6 millim. 



III! 5, shield-shaped, often projecting slightly in some or 

 all of the rays. Average measurements, deduced as above, 

 are : — Height to bottom of facet 9*95 millim. ; width below, 

 13"9 millim. ; width above, 14*9 millim. ; width of facet 8"7 

 millim. Extreme measurements, as above, are : — Height 3 

 millim. and 8 millim. ; width below, 4'2 millim. and 9"5 

 millim. ; width above, 4 millim. and 11'25 millim. ; width of 

 facet 3'25 millim. and 6 millim. The adjacent sides are 

 usually almost parallel in medium-sized specimens, and even 

 converge upwards in small specimens. From the above 

 measurements and others it appears that, while the average 

 width of the facet is "577 *, or rather more than half, that of the 

 radial, it is proportionally greater in small individuals, e. g. 

 •81 in 57o6o, and less in large individuals, e. g. '53 in 

 E 6003. The facet is sometimes more to one side of the 

 radial than the other; it is transversely elliptical in outline 

 (PI. Xlll. fig. 11). A fulcral ridge runs across, a little 

 outside the long diameter, and in the centre of this ridge is 

 the axial canal. The food-groove forms a wide depiession 

 on the inner side of the ellipse. Partly owing to the varia- 

 tion in the projection of the radials, the angle at which the 

 facet is directed outwards varies considerably even in the 

 same specimen. In the separate cups found at Klinteberg, 

 in Gotland, which lend themselves to such measurement more 



* These numbers are fractious of the width of the radial, not of a 

 milhuietre. 



