VILL. Cyathoerinus. 217 
Average measurements, deduced from six specimens, with 
allowance for variation within the limits of an individual :— 
Height 3:5 imillim.; width below, 3°7 millim. ; width above, 
4:8 millim. Extreme measurements noted are, in 57365 and 
i 6003 respectively :—Height 2 millim. and 5 millim. ; 
width below, 2°5 millim. and 4:25 millim.; width above, 3 
millim. and 6°8 millim. In E 1450, which is a medium- 
sized specimen, the height varies from 2°5 millim. in r. ant. 
1B to 3:2 millim. in |. post., |. ant., and ant. I BB. 
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, 8°5 miJlim. 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 cthers; thus, in E 1450, the measurements of 
the post.B and of the other BB are Za follows :—Height Ss 
millim, and 5:5 millim.; width below, 5°75 millim. and 5 
millim.; width above, 7 millim. and G lee 
RAR 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 i 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 57865, and less in large individuals, e. g. 53 in 
E 6003. he facet is sometimes more to one side of the 
radial than the other; it is transversely elliptical in outline 
(Pl. XIII. fig. 11). A fuleral 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 depression 
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 fractions of the width of the radial, not of a 
millimetre, 
