152 PALEONTOLOGY 



more pronounced in the earlier formed part of the last 

 whorl. It may be taken as marking the peripheral margin. 

 The ornamentation, as seen in the cast, consists of two 

 quite independent series of lines (i) a series of very 

 faint ribs, most clearly seen at the peripheral margin, 

 where they are less than i mm. apart. They are curved 

 with a forward concavity on the lateral area, and at the 

 peripheral margin they bend backwards and cross the 

 periphery in a deep curve like the hyponomic sinus 



FIG. 42. MANTICOCERAS AFF. RETRORSUM (VON BUCK), UPPER 

 DEVONIAN; BUDESHEIM, EIFEL. (x2.) 



Cast of an immature example ; the faint ornamentation omitted ; urn- 

 bilicus filled with matrix ; numerous suture-lines behind the body- 

 chamber. (Original.) 



of Nautiloidea. (2) The other ornament is a series of 

 much finer and closer irregularly-sinuous lines, about 

 five to each of the ribs, to which they are not parallel, but 

 run obliquely back from the umbilical margin in a curve 

 which is at first convex forwards and is afterwards 

 reversed. 



The suture-line (septal suture) is of a kind intermediate 

 between those of a Nautilus and an ammonite : lobes and 

 saddles are well-defined, but entirely free from frilling 

 (goniatitic type). There is a broad peripheral lobe, 



