The annals and magazine of natural history : zoology, botany, and geology . eloping and mature corallite are not at all proofs of aprimary tetramerism \ moreover, Gordon jiroduces no proofsbeyond a suggestive condition in Streptelasma profundum tobe discussed later. According to my interpretation, in theRugosa a secondary tttramerism has been impressed upon ap rim a ri/ h exa m e r is m. At first sight it would seem to be a simple matter todetermine the number of primary septa in a corallum. It is Morphology of the Madreporaria. 233 rarely, however, tluit one secures examples of these ancientc
The annals and magazine of natural history : zoology, botany, and geology . eloping and mature corallite are not at all proofs of aprimary tetramerism \ moreover, Gordon jiroduces no proofsbeyond a suggestive condition in Streptelasma profundum tobe discussed later. According to my interpretation, in theRugosa a secondary tttramerism has been impressed upon ap rim a ri/ h exa m e r is m. At first sight it would seem to be a simple matter todetermine the number of primary septa in a corallum. It is Morphology of the Madreporaria. 233 rarely, however, tluit one secures examples of these ancientcorals having perfect tips, and otherwise of such a characterthat the arrangement of the earliest septa can be made out,either from microscopic sections or grinding down. Speci-mens of Lopliophyllum proUferum^ the species first studied inthis connectiuu, are usually remarkably favourable for suchan investigation. Where, in other species, the tips areperfect, it is often found that the septa are not determinableuntil one or more metaseptal pairs have aj)peared, in addition. The interseptal spaces are now preatly enlarged, and all the septa arefree from eacli other and from the dor.^al directive septum with itscolmnella-like free end. Exosepta regularly alternate with theentosepta all round the calice, and the ventral directive septum isa little smaller than the other principal septa, thus giving rise to afossula. The stage Iepreseuted is practically that characteristic ofthe fully developed corallum. to the protosepta ; sometimes partial or entire silicification ofthe corallum has taken place, and rendered the preparationof sections practically impossible; while in such as Dancanellahoreahs the original tip is wanting, and when first collectedfour, five, or six pairs of septa are frequently exposed toview (fig. 17). Since the publication of my first paper I have made con-siderable efforts to secure from various sources specimens of 234 Prof. J. E. Duerden on the rugose corals par
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