104 
parts. It may, for the sake of convenience in noticing tbeS« 
variations, be said to be composed of three parts, a centra 
or depressed portion, crowded with cells, a raised or p r0 " 
ininent circle round the centre, formed of erect or semi-er e ® 
aggregated tubes, and a thin, plain, translucent margin d es ' 
titute of cells. 
In form it very much resembles a miniature sonp-pj 8 
It is calcareous, white, sessile, rarely exceeding half-an-io® 
in diameter, and is attached by the base of the central d e ^ 
pression. The depression varies in size from a mere P ol ° r 
to about three-eighths of an inch in diameter, and is e ' t . j 
round, or very irregularly oval. The surface is occup 1 ®^ 
by small, semi-horizontal, closely aggregated tubes, <v * 
oblique even apertures. The raised circle is also H a . g 
to great variations in form. In most cases the tubes 
abruptly from the circumference of the depression, t° r f‘ 
ing well defined lluted sides to the cup ; sometimes they rl j’ 
in gradual succession one above another, forming a ge n J 
sloping surface from the margin to the centre ; someth' 1 , 
the surface is arched concavely, at others convexly, f 
between these extremes there is every possible variati 0 ^ 
The sides of the cup are generally uniformly fluted, a f urr ° r0 
being formed by each tube; but sometimes the tubes a j- 
arranged in companies, and then, the sides appear form® ^ 
fluted columns. The tubes are of equal diameter and i e 
in a greater or less degree, obliquely outwards. The ap 
tures are generally on one plane, but occasionally r ,se 
radiating ridges; but some will rise singly above the oth e ^ e 
The apertures are even and oblique ; but sometimes, if 
specimen be examined as soon as it is taken, the aperh'j^ 
appear armed with one or two spines, hut this appears to ^ 
the result of the greater growth of one side of the lip l h a j Jt ,y 
the other, for their situation is by no means constant, 1 s 
are often absent, and always form a continuation of the s jy 
of the tubes. The third or external part is freq«® 
wanting. In its greatest developement it is about as «'i , 
the middle or raised circle of tubes; it is calcareous, 11 
lucent, very thin and radialingly striated with the rud 1 * 11 ^^, 
of tubes, which are thickly arranged, though never in c ° ! ^ aC b 
They however sometimes branch and anastomose with 
other. In a very recently formed portion of this n ‘ ar ” 
these tubes do not extend quite to the circumference, “ ] 0 
age advances they get more and more elongated till the -ft 
surface is permeated by them; so that at first they a P,j-j,al 
pointed hut afterwards of equal diameter throughout. 
portion of the surface which is next the circle of 
always occupied by partially formed apertures ot ne»v ,^\\ 
and from examining large numbers of specimens > r ° 
