6 THE DEVONIAN OF MISSOURI. 



below the shales is profound, and above they grade into the 

 Louisiana limestone of the Mississippian without any indication 

 of unconformity. 



The evidence from fossils indicates a Devonian age for the 

 shales but the evidence is not strong. A group of fishes is present 

 that has not been identified from rocks above the Devonian but 

 in some cases the presence of these fishes was made the basis 

 for identifying the rocks as Devonian. The species present in 

 the Grassy Creek shales are, with two exceptions, different 

 from those in other areas. The exceptions are Ptyctodus calceolus 

 (Newberry and Worthen) -and Dipterus mordax Eastman. But 

 Ptyctodus calceolus (Newberry and Worthen) is widespread in 

 the Sylamore sandstone of central Missouri which is without 

 question of Mississippian age. The armored fishes present 

 belong to the genera Dinichthys and Mylostoma. These genera 

 lived usually in seas in which black muds were being deposited 

 and do not occur in abundance anywhere. They are unlike the 

 sharks, which are relatively independent of bottom conditions 

 and leave their remains in all sorts of waters. The pavement 

 toothed sharks were just coming in during Grassy Creek time 

 and they are not distinguishable from those from the Chouteau. 

 The invertebrates are mainly Lingulas belonging to new species 

 and are of little value for correlation purposes. Greger 1 identifies 

 the following species in the fauna. 



Ptychostylus subtumidus Gurley 

 Lingula missouriensis Rowley 

 *Lingula pikensis sp. nov. 

 Lingula tantilla sp. nov. 

 Lingula rowleyiana sp. nov. 

 Lingula insolata sp. nov. 

 Lingula yatsui sp. nov. 

 Lingula conklini sp. nov. 

 Athyris bransoni sp. nov. 

 Adolfia cf. amarus Swallow . 

 Douvillina cf. mucronata Conrad 

 Palaeonila compressa sp. nov. 

 Pterochaenia longwelli sp. nov. 



*The new species have not been described or figured. 

 'Bulletin, Geol. Soc. Am., vol. 29, p. 95 



