stony fronds, and of various uncertain shapes, found encrusting 
tidal rocks, and occasionally thrown up or dredged from deeper 
water. Dr. Johnston’s figures, at Plate XXIV. 1, 2, 3, of his 
‘History of British Sponges and Lithophytes,’ represent a form 
which abounds in Dalkey Sound, near Dublin, and on which the 
late Mr. M‘Calla founded a species which he called Nu/lipora com- 
pressa. It perhaps ought to receive a specific name, but, if left 
unennobled, it seems to me rather to fall, as a variety, under 
M. calcarea, than under the present species. 
Fig. 1 and 2, different specimens of MELOBESIA POLYMORPHA :—the natural 
size. 8. Small portion of a fertile frond, showing the ceramidia. 4. Vertical 
section of the frond, to show arrangement of cellular coats :—both magnified. 
5. Cellular structure :—highly magnified. 
