338 THE FOKAMINIFEKA OF THE EXE ESTUARY. 



On the Polesaiids, above and immediately below low water, there 

 are practically no living Foraminifera. 



Stranded on the onter or seaward slopes of these sands the following 

 dead shells were found ; no attempt has been made to estimate the 

 relative numbers. MiUolina seminulum. 



Truneatulina lohatula. 



Rotalia heccarii. 



Nonionina depressula. 



Polystomella crispa. 



PohjstomelJa striato-pundata. 



On the northern or estuarine slope of these sands even dead shells 

 are absent. 



The method of investigation adopted consisted in spreading 13 c.gms. 

 of each sand on a glass slip and counting and identifying the Fora- 

 minifera. 



This process is not exhaustive, as small specimens and species may 

 be overlooked, no matter how carefully the sand may be spread. Also 

 the less common species cannot be expected to be represented in each 

 13 c.gms. Accordingly fifty times this quantity (6*5 gms.) is taken, 

 and the Foraminifera floated from same as far as may be. Invariably 

 additional species are thus found. The drawback to this proceeding 

 lies in the fact that the numerical results are no longer absolute. No 

 doubt the direct count gives results in themselves too low, but at least 

 fairly comparable as between the species identified. In floating, how- 

 ever, only a small proportion of the Foraminifera of any species are 

 obtained, and the relative numbers of the different forms depend largely 

 on the weight per unit displacement of the individual species. Thus 

 Rotalia heccarii floats extremely ill, and Polystomella striato-punctata 

 fairly well. The effect from actual averages is as follows: Assume 

 a case in which 1,000 of each of the following species are counted in 

 a sample, then on floating we should obtain the following numbers 



only : — * For each 1,000 found by 



actual count. 



Pulystomella striato-punctata . . 170 or 17 per cent. 



Biloculina ringens . . . 167,,16"7 „ 



Planorhulina mediterranensis . . 73 ,, 7*3 ,, 



Nonionina depressula . . . 36,, 3'6 ,, 



Bulimina pupoides . . . 30 ,, 3 ,, 



Miliolina seminulum . . . 13 ,, 1'3 ,, 



* It should be noted that the figures given are the average of a large number of observa- 

 tions ; but when, as at Exniouth, a great jH-oportiou of each species is represented by small 

 individuals, the actual percentages which float will be much greater than given in the 

 table, the relative percentages remaining constant. 



