DISC 'I r SSION. 



Professor Dr. Zittel: I consider the fossils exhibited by Mr. Walcott 

 to be dermal plates and scales of fishes. They differ considerably from 

 everything hitherto known from -Silurian strata, and show a decided 

 resemblance to Asterolepis and Holoptychius of the Devonian rocks. 

 Microscopic slides are needed to show with certainty the osteoblasts and 

 the peculiar structure of the dermal ossifications of fishes. 



Dr. .Frederick Schmidt: 1 agree with Professor Zittel that the fossils 

 are undoubtedly fish remains. 



Professor E. W. Claypole: before we can admit the existence of fishes 

 during so early a period as the earlier Silurian, it will be necessary to 

 use every means to prove the ichthyic character of the remains, especially 

 the study of microscopic sections. 



Professor E. D. Cope: It is very doubtful whether the remains of 

 crossoptergyian fishes occur at so low a horizon. I consider it essential 

 that the skeleton should he found before deciding that fishes were pres- 

 ent, as the dermal covering of the lower vertebrate is not a reliable char- 

 acter in classification. 



Mr. Walcott: Microscopic sections are being made and will he fully 

 described in a final paper.- Moreover, Mr. S. Ward Loper is collecting 

 material in Colorado at the present time that may add materially to our 

 knowledge of the fauna. 



Dr. Otto Jaekel : The remains in their exterior characters do not 

 recall the fish remains known from flu 1 Upper Silurian, but rather those 

 of the Old bed sandstone. The resemblance to the latter becomes still 

 more striking for the reason that the two appear in the same kind of 

 rock and in like condition of preservation ; but on closer comparison of 

 the two it appears that the agreement is by no means so great as would 

 seem at first sight. The forms resembling each other cannot he identified, 

 and the fauna here spoken of exhibits types of microscopic structure 

 that are as foreign to the Devonian as to the upper Silurian. Still, this 

 much seems certain : that the pteraspidse and acanthodians, dominating 

 in the uppermost Silurian, are absent from this fauna ; whereas, on the 

 other hand, they ally themselves with the Devonian remains of Crosso- 

 pterygea and placoderms and of true ganoids. Not a single fragment 

 shows any resemblance with the placoid parts of the elasmobranchii. 



* In response to an invitation from Mr. Walcott to discuss briefly the 

 micro-structure of the fish remains, 1 may observe, as regards the histo- 



■ \ni irnmunieated after examining the slide! 5 made from the fossils. 



(168) 



