ORDER ACTINOIDEA. 49 
lamelle meet at a small angle and coalesce. This proceeds from 
a slight distortion of the circular animal, and is most common in 
species which have the lamelle undulated, by which irregularity 
they are often brought into contact. When the Fungia retains a 
perfectly circular form, this union of lamelle is seldom observed. 
It is not unusual for the lamelle in an Actinia to grow together by 
their edges when in contact. 
6. The number of tentacles in this group, or the number of lamelle, 
is very commonly a multiple of six. In one division of the Astras 
(the Orbicelle), we find the numbers 18, 24, 36, 48; in other species 
of the genus, the mode of indefinite increase and subdivision, pre- 
vents our ascertaining how nearly they correspond. The Oculine, 
Dendrophylliz, and Caryophyllie conform generally to the same 
series, and so also the Madrepores and Antipathi, which contain 
twelve and six tentacles respectively. 
In many instances, however, four is a submultiple, and this is 
shown by the lobed margin of the Lucernarie, and the divisions in 
the mouth of some Actinie. ‘That this should often be the fact is 
apparent from figure 15, § 25, in which one larger and three smaller 
intervals alternate; and it appears that generally when a multiple of 
siz, the numbers are also multiples of four. 
While, therefore, the Alcyonaria have ezght equal lamelle, the 
Actinaria may have sez or twelve equal lamella, or a number of un- 
equal lamelle, exceeding twelve, which isa multiple of four or siz. 
The mouth and margin of some Actinie is five lobed; but these may 
still conform to this principle. In the Antipathi, there are six equal 
tentacles; in the Madreporacea, twelve tentacles, with six alternate, 
often distinctly larger than the others: and the calcareous lamell of 
the cells, in other species, are usually either alternately large and 
small, or one large alternates with three smaller, or one with five 
smaller. 
There is, moreover, in the Actinaria, a relation between the size of a 
polyp and the number of its internal lamelle. In many Astreas, 
there are fourteen or fifteen—large and small—to a breadth of a 
quarter of an inch; and, where the number has the above relation, 
18, 24, 36, 48, there is nearly the same relation in the diameter of the 
cells of the corallum. This relation admits of considerable variation, 
which is sometimes seen to be dependent on a part of the lamelle 
being obsolescent. ‘The Astrea hyades and A. pleiades both have 
twenty-four lamelle to the cells; but in the former, which has the 
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