(a) Red Beach Cave.

The cave at Red Beach measures 18 metres from mouth to vertex, and 3 metres at the highest part of the entrance. The floor is 1-2 metres wide, its lowest level being slightly above E (H.)L. W. N. (Figure 1A). As mentioned before, it faces approximately N. 60° E. Relative humidity (measured by using a whirling psychrometer) at 2.0 p. m. on 6.2.50 was 75% inside the cave, as against 57% outside in broad daylight (air temperature 23 0° C.). Unlike the situation in the caves examined by Lami, there was no appreciable difference in humidity measurements in different sectors. Overarching of the south-east wall at the entrance to meet up with the north-west wall, which is more or less vertical, is responsible for cutting off direct sunshine from it during mid-summer. The north-west wall, in spite of receiving less direct sunlight than the south-east wall in winter, is more strongly lit than the latter by continuous, diffuse daylight. The light gradually loses intensity until in the ultimate recesses the meter fails to register and it is almost completely dark. The fact that Sabellaria penetrates a greater distance on the north-west wall may be correlated with the greater degree of penetration of indirect daylight on that wall (ef. Figures 3, 4). By contrast, at upper levels on the south-east wall Nodularia and Rhodochorton each occupy a narrow belt, but Rhodochorton is absent from a corresponding position on the north-west wall. Tethya, too, is confined to darker crannies, though nearer E.(H.)L. W. N. On both walls Hildenbrandtia gradually assumes complete dominance at all levels beyond 10 metres in from the mouth. The more recent visit in December, 1952, revealed the presence of Mitella spinosa, a dark brown, stalked barnacle on the south wall at 10 metres, in almost total