162 PEOF. W. J. DAKIN : EXPEDITION TO THE 



Hauls with the dredge were made several times just outside Recruit Bay, 

 with a depth of 20 fathoms. We finished up to the N.E. with a sandy 

 bottom and an abundance of. seaweed. Large hauls of sponges were made 

 here, and compound Ascidians and Echinoderms, including Synapia sp., were 

 present in considerable numbers. Echinoderms were always well to the fore 

 so far as individual numbers were concerned. Crustacea were only 

 moderately represented, being chiefly Brachyura and Alpheids, which 

 abounded in the crannies of the coral rocks brought up in the dredge. 

 Macrura were not common on the whole. 



A few dredge hauls were made east of Evening Reef in a rather rough 

 sea. The bottom was of sand and small fragments with much weed. A few 

 Echinoderms were obtained, including a fine Astrophyton. 



THE EASTER GROUP. 



The Easter Group differs in several respects from the group of islets we 

 have just been considering. In the first place it has much more the aspect 

 of an atoll with an island in the middle of the lagoon, the total area of the 

 atoll measuring about 35 square miles. 



The central island is Rat Island, (2 or 3 small islets which lie to the south 

 and are separated by narrow channels a few yards across — dry at low tide — 

 may be considered as part of it), and a glance at the chart (text-fig. 8) will 

 show that the surrounding reefs encircle it in quite a regular manner 

 at a distance varying from 2-5 miles. A gap occurs in the reefs to the 

 south of the group, and they are not well developed to the north-west 

 and north. In other words, the larger entrances to the lagoon are to the 

 north and north-west. We shall see later that this agrees with the Pelsart 

 Group. It will be remembered here that encircling reefs were similarly best 

 developed to the south of the Wallaby Group, whilst the chief entrances to 

 the lagoons opened to the north. 



The encircling reef to the west of Rat Island does not bear any islets 

 above sea-level at high tide. There are several islets, however, on the eastern 

 rim forming a chain upwards of eight miles in length. This development 

 also agrees perfectly with the character of the more southern group of 

 the Abrolhos. Each group of islets is evidently being modelled by the 

 same forces and conditions. The depths of water in the lagoon of the Easter 

 Group range from 2-22 fathoms, there being quite considerable depths 

 on the eastern side of Rat Island between it and the islands of the rim. 

 Before considering, however, the lagoon and the coral reefs, let us glance at 

 the central islet — Rat Island. This is the largest island of the Easter Group, 

 but it is smaller than either of the two Wallaby Islands, being only a little 

 over f mile long (from N. to S.) and not half a mile broad. 



The small islets to the south of Rat Island are four in number and are 



