No. l.J J. W. DAWSON — PAL^ONTOLOGICAL NOTES. 3 



The siphuncle, which wants a portion of the apex, is a flat, 

 tened cone, which, when complete, must have been about 5^ 

 inches in length, and 2J- in its greatest diameter. It is marked, 

 in the portion preserved, with about twelve diagonal ribs, indi- 

 cating the lines of attachment of the partitions of the external 

 shell, of which only portions of a few remain attached to the 

 surface at one side. The lower part of the shell is divided by a 

 vertical partition crossing its longer diameter. At the top this 

 splits into a flattened cone, somewhat flatter than the siphuncle 

 itself, and more obtuse, so that at the top it joins and unites 

 with the rim of the siphuncle, The space below this inner cone 

 is that supposed to have been solid ; but in the present specimen 

 it is filled with calcite, showing that it must have been an en- 

 closed space. Farther the vertical partition presents, in section, 



Fig. 2. — Transverse and restored vertical sections of Piloceras amphim 

 reduced. The upper figure shows the proportions of the 

 cross section. The lower figure is a section in the direc- 

 tion of the shorter diameter, showing the conical siphuncle, 

 the siphuncular cavity, with remains of partitions, and the 

 external chambers. The dotted lines are restored portions. 



