stony fronds, and of various uncertain shapes, found encrusting
tidai rocks, and occasionaiiy thrown up or dredged from deeper
water. Dr. Johnston’s figiues, at Plate XXIV. 1, 2, 3, of his
‘ History of British Sponges and Lithophytes,’ represent a form
which abounds in Dalkcy Sound, near Dublin, and on which the
late Mr. M'Calla founded a species which he called Nullipora compressa.
It pcrliaps ought to receive a specific name, but, if left
nnennoblcd, it seems to me rather to fall, as a variety, under
M. calcarea, than under the present species.
Fig. 1 and 3, different specimens of Melobesia polymoepha :— the natural
she. 3. Small portion of a fertile frond, showing the ceramidia. 4. Vertical
section of the frond, to show arrangement of cellular coats :—both t
6. Cellular structure —highly magnijied.