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 all 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 



