262 JAMES PER R IN SMITH AND STUART WELLER 



The only species with which Prodromites ftraematitrus might be com- 

 pared is P. gorbyi, from the same horizon ; but in P, praematurus the abdo- 

 men is slightly broader, the shell rather thicker, the septa rather more 

 complex, and the umbilicus slightly wider than on P. gorbyi at the same 

 diameter. In the figures and the descriptions of the septa a difference 

 between the two species may easily be seen. 



DIMENSIONS 



Diameter .... ... 62 ,n;n 



Height of last whorl ------ 34 



Height of last whorl from the preceding - - - 21 

 Width of last whorl ------ g.5 



Involution - - - - - - - 13 



Width of umbilicus ------ 6.5 



This specimen was septate throughout, so the length of the body cham- 

 ber could not be ascertained. 



Only a single specimen is known, No. 6223, of the Paleontological Col- 

 lection, University of Chicago, from the Kinderhook goniatite limestone of 

 Rockford, Indiana. 



CONCLUSION 



In Prodromites we have the oldest known ammonite and the 

 most complex ammonoid yet described from strata older than 

 the Permian, occurring only a short distance above the base of 

 the Lower Carboniferous. In all probability the ancestors of 

 this genus had already become ammonites before the close of 

 the Devonian, but we do not know where to look for them. 

 The Kinderhook ammonoid fauna is exotic in America, and 

 seems to be exotic wherever it is known. But in the faunal 

 region from which this migration came we may expect to find a 

 highly specialized fauna of which those forms that made their 

 way into Europe and America in Tournaisian time are but a 

 fragment. We have, as yet, no clue as to where this region 

 was, but the vast unexplored Paleozoic stretches of Asia lead us 

 to hope for much new information when that continent shall be 

 thoroughly investigated. 



The occurrence of such forms as Prodromites, without local 

 ancestors serve only to emphasize our ignorance of the ancient 

 zoology of regions outside our own, and should stimulate 

 research in geographic distribution of fossil faunas. 



