348 LOUIS AGASSIZ. 



lows : As soon as the number on the species 

 of the " Old Red ' ' is finished, I shall complete 

 the general outline of the work as I did with 

 volume 4, in order that the arrangement and 

 character of ah 1 the families in the four orders 

 may be studied in their zoological affinities, 

 with their genera and principal species. But 

 as this outline can no longer contain the in- 

 numerable species now known to me, I take 

 up monographically the species from the dif- 

 ferent geological formations in the order of 

 the deposits, and publish as many supple- 

 ments as there are great formations rich in 

 fossil fishes. I shall limit myself to the species 

 described in the body of the work, merely 

 adding the description of the new species 

 in each deposit, and such additions as I may 

 have to make for those already known. In 

 this way, those who wish to study fossil fishes 

 from the zoological stand-point can turn to 

 the work in the original form, while those 

 who wish to study them in their geological 

 relations can confine themselves to the sup- 

 plements. By means of double registers at 

 the end of each volume, these two distinct 

 parts of the work will be again united as a 

 complete whole. This is the only plan I have 

 been able to devise by which I could publish 



