287 



and my inshore collections were all probably very much nearer 

 the shore than any of his were made. It is therefore legiti- 

 mate to omit these inshore collections in comparisons based 

 on amounts under one square meter. Accordingly, if we omit 

 Nos. 1, 8, 9, and 10, the probable error of distribution becomes 

 ±15.4 per cent., with a range of —25.2 to +34.2, a total of 

 59.4 per cent, between limits. This is far within the limits of 

 error which Reighard's St. Clair data yield. Since his catches 

 include two at depths of 1.17 m., we may include all of my 

 catches except No. 10, in which case the probable error of dis- 

 tribution rises to ±38 per cent., with a range of —77.1 to 

 + 71.7, a total of 148.8 per cent., Reighard's data yielding on 

 this same basis of computation ±31.8 per cent., — 57.5 to 

 + 111.5, and 169 per cent. The greater average ± error of 

 distribution in my river test when these lateral collections are 

 included is manifestly an expression of the effect of shore — an 

 element not so pronounced in Reighard's tests. On this basis 

 the limits and total range still remain less in the river test 

 than in the lake. 



From the data of transverse distribution in the Illinois 

 River it is apparently demonstrated that, on the whole, the dis- 

 tribution is no more variable than it is in Lake St. Clair; and 

 if we eliminate marginal collections and consider only channel 

 waters, that is the middle two-thirds beyond 20 meters from 

 shore, the variation falls considerably within the margin of er- 

 ror found in the lake, being in the six centrally located col- 

 lections ±15.4 per cent, on computations per square meter of 

 surface, and ±24 per cent, for the same on the basis of plank- 

 ton per cubic meter. 



The variation was also tested by counting the planktonts 

 in the catch, with the resulting error in distribution of ±7.8 

 per cent, for all ten catches, with limits of —14.7 and +31.8 — a 

 total of 46.5 per cent. 



The cross-section made below the mouth of Spoon River 

 September 30, 1897, contains ten collections made at equal dis- 

 tances, about 12 meters apart, and the first and last this same 



