of the Transition Formations of the Rhine, 1 7 



The drawing given by Bronn in the ' Lethaea geognostica' has 

 certainly not been taken from nature, but probably from the 

 description of H. von Meyer. The Gyroceratite of the latter is 

 certainly only referrible to this fossil. Bronn gives as a syn- 

 onym a Lituites gracilis, Goldf. Collect. ; certainly there is 

 in the Museum at Bonn a fossil designated as Lituites, but it 

 is another fossil : it presents no chambers, and I think is a 

 cast of Euomphalus, perhaps Eu. Icevis, Goldf. 



With regard to the increase in height and in breadth, the 

 A. compressus is very near the A. Dannenbergi', it is princi- 

 pally distinguished from this by the simple lobes, and it never 

 attains the size of the latter. There are neither ventral nor late- 

 ral lobes in this species ; this Ammonite has in common with 

 A. lateseptatus the simplicity of lobes. In the specimen 

 figured PI. I. fig. 6. there is a portion of the part without 

 chambers preserved. It may be very distinctly seen, by the 

 striag upon the shell, that it was very thin. 



The species described here, to which A. expansus, von Buch 

 is nearly allied, form a group among the Goniatites, limited 

 in a very natural manner. Except the dorsal lobe, which can 

 always be very distinctly seen, there is nothing very particular 

 to be said about the lobes. There is only a very slight in- 

 flexion of the transverse plates, that in every individual occu- 

 pies the entire side quite to the suture. We cannot arrange 

 here with certainty any of the Goniatites of the old transition 

 limestone of the Fichtelgebirge described by Count Miinster ; 

 A. latus and A. angustiseptatus can only be added to this sec- 

 tion as doubtful species. 



Section II. Simplices. 

 The dorsal lobe simple, infundibuHform or linguiform. 

 There is a lateral lobe more or less angulose, and a broad late- 

 ral saddle occupying the greatest part of the side. 



5. Ammonites retrorsm. Von Buch. PI. I. fig. 10. a, b, c, 

 L. de Buch Goniat. p. 49. PI. II. fig. 13. 



The dorsal lobe small, infundibuHform, almost as broad as 

 deep. The lateral lobe is rounded beneath, more than twice 

 as deep as the dorsal lobe, and a little broader than deep. The 

 lateral saddle, broad and rounded, is also raised to the dorsal 



Ann, Nat. Hist, Vol.3. No. 14. March IS^9, c 



