MARINE BIOLOGICAL STATION AT PORT ERIN. 25 



done to some extent with the "Fauna" of Liverpool Bay, 

 and the following instances may be taken as samples. 



The known number of species of higher Crustacea in 

 Vol. I. of the " Fauna " (1886) is 90, and these fall into 60 

 genera. But many species have been added since then, 

 so Mr. Walker has gone over the records up to date (1895), 

 and states that we now know in our local fauna 230 

 species which belong to 150 genera. This is still much 

 the same proportion as in the former numbers, so we may 

 take it that in our district the genera are to the species as 

 2 to 3, whereas in the collections quoted from Mr. Walker 

 above the genera are to the species on the average about 

 as 28 to 31, or nearly 7 to 8. It can also be brought out 

 by similar series of numbers that as one extends the area 

 investigated the number of species per genus is increased. 

 In a single haul, in our district as we have seen, the species 

 are to the genera about as 8 to 7, in our local fauna the 

 proportion is about 3 species to 2 genera, while in the 

 much wider area embraced by Sars' Amphipoda of 

 Norway the numbers are 365 species to 157 genera or 

 nearly 5 species to 2 genera. In other words if allied 

 species, taking a large district, were associated together 

 we might expect to find about twice as many species per 

 genus in each haul as we do find. 



Mr. Walker has gone carefully into this matter of the 

 proportion of genera to species in our hauls, and in other 

 areas, and from the figures in his notes I extract the 

 following records, in support of the above statement : — 



Ehos Bay, 13/5/93, Amphipoda, 16 sp. in 14 genera. 



Little Orme, 28/7/93, Amphipoda, 24 sp. in 22 genera. 

 5/10/93, „ 29 „ 24 „ 



The aggregate of the species and genera of Amphipoda 

 in the above three dredgings is 69 species in 60 genera, or 

 an average proportion of 115 ; 100. Now the total number 



