LAGOON DEPOSITS. 



583 



So far as I am aware this is the first recorded occurrence of a true pelagic deposit, 

 i.e. Pteropod Ooze, within the lagoon of an atoll. It is accompanied by much fine matter, 

 the inorganic part of which consists almost entirely of carbonate of lime. The Challenger 

 Report recorded the presence of a similar deposit off many coral reefs and oceanic islands, 

 that around the Fiji Group being particularly noticeable, though in my own experience it 

 is not found in the lagoons of the atoll or barrier reefs of those islands. The presence of 

 this deposit in Suvadiva lagoon at depths over 40 fathoms is interesting as it is not found 

 elsewhere in the shallower lagoons we investigated, and it would naturally be expected that 

 the calcareous remains of such small pelagic organisms would have been rapidly dissolved 

 in the sea-water and removed. A considerable proportion of the deposit being formed of casts 

 shows that its origin cannot have been due to merely temporary causes. It might reasonably 

 be deduced that the lagoon of Suvadiva below 35 or 40 fathoms is a relatively still one 

 \vith little circulation in its sea-water, but the reason of this state is not obvious, as that 

 atoll has 38 well-defined passages into its lagoon, of which 7 are about or over 35 fathoms 

 in depth, and 17 about or over 20 fathoms. It is useless, however, theorising on the subject, 

 when it is obvious that practically nothing is known of the physical conditions of this large 

 lagoon. In connection with the question it will be interesting to see what deposits Prof 

 Agassiz found around the Maldive banks at moderate depths. The presence or absence of 

 manganese nodules or deposits, indicated in no. 24 below, will no doubt be considered also by 

 the same author. 



I have appended a chart to Sir John Murray's Report (PI. XXXIV), underlining the 

 positions from which the samples from Suvadiva atoll were obtained. I add from the same 

 Report a list of the animals of such groups as will other\vise not be treated of in this 

 publication. Names in brackets have been added by me, the bracketed genera of the 

 Foraminifera having been kindly identified by Mr J. J. Lister. 



Pelagic Foraminifera : 



Glohigerina aequilateralis. 



„ dubia. 



Orhulina universa. 

 Sphaeroidina dehiscens. 

 PuUenia obliquilucidata. 



Glohigerina buUoides. 

 „ saccidifera. 



„ conglobata. 



„ digitata. 



rubra. 



Pulvimdimi tumida. 



„ menardii. 



„ canannensis. 



Cy nibalopora. 



Bottom Foraminifera : 



Bilocidina. Rheophax. 



(Miliolina). ( Textidaria). 



Spirolocidina. Cassidtdina. 



Feneroplis. Lagena. 



(Orbitolites). JS'odosaria. 



(Alveolina). 

 Mollusca Pteropoda: 



Clio subula. 

 ,, australis. 

 Mollusca Heteropoda : 



Atlanta. Carinaria. 



Other Mollusca: 



Pleurotoma. Dentalium. 



Diatomaceae : 



Pleurosig ma. Surirella. 



Polymorphina. 



Uvigerina. 



PuUenia sphaeroides. 



Rotalinae. 



Polytrema. 



Limacina. 

 Cavolinia. 



(Gypsina). 



Amphistegina. 



{Polystomella). 



(Operctdina). 



H eterostegina depressa. 



{Oxygurus). 



Coscinodiscm. 



{Pterotrachea). 



