INHABITING MULTILOCULAR SHELLS. . 47 
thus feel warranted in concluding that a corresponding alteration ex- 
isted in the structure of the animal inhabitant. We then proceed to 
subdivide these larger into smaller and more convenient groups, and 
consider the external appearance as a sufficient generic character, 
because on that chiefly seems to depend the fact whether the body of 
the animal was included within the shell or included it. Bearing in 
mind this distinction, there may be mentioned five well-defined and 
easily-known genera of Ammoneata, which are called Turrilites, 
Scaphites, Ammonites, Hamites, and Baculites, all having a dorsal 
siphuncle, and its walls of separation between the chambers being 
in all more complicated, and stronger than is generally the case in 
any genus of Nautilacea. As in that family we first explained the 
mere technical facts relating to each genus, and then enlarged a little 
on the probable nature of the animal, so we propose now, following 
the same course, to inform the reader, first, of what is Known with 
regard to these extinct genera; and then to indulge in some of those 
curious speculations which the subject is so well calculated to 
introduce. 
The order in which we have arranged the known groups above- 
mentioned is not of much consequence, perhaps ; but, as it departs 
from that usually employed, we may as well observe that the names 
are not thrown together thoughtlessly, but arranged on a principle 
which, for our purpose, is convenient enough. First, taking the 
most complicated form, we have named the Turvrilite, which is a 
spirally twisted shell, not developed on one plane. In fact, its shape 
resembles that of a Snail, and many other common turreted shells, 
too well known to require mention. The next, Scaphite, is named 
from a Greek word signifying a boat, and may be compared to an 
Ammonite whose last whorl is separated from the rest, and after 
being extended for a short space ina straight line, is again bent round 
to meet the rest of the shell. The Ammonite isa simple spiral, with 
the whorls contiguous and developed on one plane ; the Hamite more 
resembles a hook (whence its name), the whorls not being contigu- - 
ous, and the Baculite (so called from its similarity to a staff), is 
quite straight, and usually in the shape of a long right cone with an 
elliptic base. 
The Turrilites, and indeed all the other Ammoneata, except the 
Ammonites, are confined to very narrow limits of geological distribu- 
tion, being rarely found in any formation anterior to the lower green- 
sand, though they do occasionally appear in the oolites. There is 
one species of Turrilite described as occurring in the coral rag of the 
