1899.] CORAlLIIUiE OF MA.DEIBA. 61 



and the spread of the branches is nearly the same. The ramifi- 

 cation is so dense that the coral resembles the thickly-leafed 

 branch of a tree. In several places one layer of branches stands 

 in front of another layer, but in both cases the polype-cells are on 

 the anterior faces of the branches. The longer axis of the broken 

 end of the stem measures 17 millim. There are three main 

 branches, one of which has been broken oif short, and this gives 

 the coral a lopsided appearance. Here and there the main 

 branches widen out in an irregular manner. This may probably 

 be owing to the fact that boring animals have excavated the axis 

 at these places, for in the lower part of the stem such excavations 

 are seen where the spiculiferous coanenchyma has been removed. 



Upon the specimen were seated some interesting zoophytes that 

 rarely occur at Madeira — (1) a branched Alcyonarian (probably 

 Suheria sp.), 100 millim. high with a spread of 80 ; (2) four fine 

 specimens of a Desmophyllum ; (3) an example of the rare Stenella 

 imhricata (J. Y. J.), 50 millim. high, with three or four branches. 



3. Pletjkocoeallium johnsoni (Gray). (Plates VI. & VII. 

 figs. 2 & 5.) 



Since this species was shortly described by Dr. Gray as a member 

 of the genus Corallmm (P. Z S. 1860, p. 127) from a specimen 

 sent by me to the British Museum, larger and more perfect 

 examples have occurred which supply materials for a completer 

 account of it. In an Additional Note on this coral (P. Z. S. 

 1867, p. 125) Dr. Gray proposed two new genera, PUurocorallium 

 and Hemicorallium, assigning the present species to the latter. 

 Later naturalists, not being able to find grounds for two genera, 

 have abandoned one of them and placed the then single species of 

 Hemicorallium under Pleurocor allium, as the definition of this 

 genus in the Note cited preceded that of the other one. (See 

 Stuart O. Ridley's valuable paper on the arrangement of the 

 Coralliidee, P. Z. S. 1882, p. 222.) 



When fully grown, the coral is much and very irregularly 

 branched with an open system of ramification, the flexuous 

 branches extending essentially in one plane, rarely meeting and 

 uniting. Base spreading widely and thinly over the object to 

 which it is attached. Axis compact, stony, white, the surface 

 striated longitudinally ; its transverse section elliptical. Cortex 

 (coenenchyma) cream-coloured, frequently pitted ; at the inner 

 surface a ring of ducts (coenosarcal canals) surrounds the axis. 

 Polype-cells prominent, sessile, wart-like, sunheDiispherical, about 

 2 millim. high and 2*5 in diameter ; irregularly scattered on the 

 anterior face of the branches from 1 to 5 millim. apart, some- 

 times in contact, especially at the tips of the branches, which are 

 knobbed with them. The summits have a cycle of eight short 

 lobes, which in the dry state curve over the orifice. The polype 

 has an orange or yellow colour. 



Only three forms of spicula have been detected in the cortex 

 and polype-cells : — (1) the double carafe-shaped spicule with two 



