Ill 
must be obtained, before we can form any opinion respecting the cir- 
cumstances in the economy of the animals inhabiting them, which 
have demanded these particular modifications. 
The fossil shells of this genus are, I believe, always found imbedded 
in a matrix, excepting those fragments of the straight part which are 
perhaps not to be distinguished from orthoceratites, the genus which 
must next employ our attention. Spirulites are found in chiefly a 
reddish marble, in Mecklenbourg, in some parts of Normandy, and, 
it is also said, in Switzerland. 
But they are obtained, by far most frequently, from Gothland and 
Oeland : the latter place affording the finest specimens : those in 
which the spiral part of the shell is preserved are very rare. The one 
which is figured Plate VI. Fig. 11, is from Oeland, and was pur- 
chased from the Calonnian collection. In this specimen, not only are 
the spiral turns of the shell seen, but traces of the continuous shelly 
siphunculus also are evident, Plate VII. Fig. 18, in a dark red lime- 
stone, evidently containing a large proportion of iron ; in which is 
displayed the spiral termination, and a small part of the straight por- 
tion of the last turn of one of these shells. Plate VII. Fig. 19, re- 
presents another of these fossils, imbedded in grey marble, from some 
part of Germany. 
LXXIV. Orthocera. A straight or slightly bent, rather conical, 
multilocular shell; the chambers separated by transverse curved 
septa, pierced by a tube. 
The shells of this, as well as those of the former genus, were placed 
by Linnaeus under the genus Nautilus ; the considerable difference, 
which is observable in their external form seems, however, fully to 
warrant their separation. Most of the shells which, though straight, 
have been considered by Linnaeus, and other naturalists, as nautili, 
are minute and even microscopic shells ; and, when sufficiently exa- 
mined, some of them may be found to possess characters distinctive 
even from both those of Nautilus and Orthocera. These are, N. ju- 
