336 
SUPPLEMENT. 
concludes by recalling Bronn’s opinion^ that if Ascoceras could be 
proved to have thrown off some of its septa at an early stage, then 
Orthoceras may be taken as the ancestral form of Ascoceras, and not 
vice versa, as held by Barrande“. 
Although Dr. Lindstrom’s discovery shows that Ascoceras began 
with a simple Orthocei'as-like shell, yet the strange and withal 
sudden transformation in its structure, by which it assumed a sac- 
like shape, with an extremely irregular septation, remains as inex- 
plicable as before. ^^"o doubt, as Dr. Lindstrom remarks, this 
alteration in the shell was due to important structural and functional 
changes in the animal. 
NOTE ON A SPECIMEN OF ORTHOCERAS 
ANNULATUM, SOWERBY^ 
A very fine example of this species from the Wenlock of Dudley 
has lately been added to the Collection. The fossil consists of the 
septate part of the shell, very much crushed ; it measures 1 foot 
5| inches in length, 1| inch at the larger and 4 lines at the 
smaller extremity. Owing to the shell being crushed, the siphuncle 
is exposed to view for the space of about 5 inches of the upper part 
of the specimen. The lower or apical portion of the shell is covered 
with the matrix; but in the centre, where this has been removed, the 
annulations are very distinct, becoming, however, almost obsolete 
above. Some of the test is preserved, and shows the finely fim- 
briated surface characteristic of this species. 
Neues Jahrbuch fiir Min. &c. 1855, p. 283 (footnote). 
^ “Ascoceras, prototype des Nautilides,” Bull. Soc. Geol. de France, 1855, 
ser. 2, tom. xii. p. 157. 
^ See ante, p. 53. 
