292 Mr. Toulmin Smith on the Classification 
the carapanulate envelope, to which the projecting points of the 
plaits were affixed, securing it without. The size of the internal 
cavity varies in different specimens, as will be seen by figs. 12 
and 13 of PI. XIV. ; of which fig. 12 is a general view of the 
external aspect of one specimen; fig. 13 is a section, with the 
matrix cleared away from the inner funnel-shaped simple mem- 
brane, of another. 
There is certainly no form among the Ventriculidse which 
might, at first sight, be less supposed than the present to have 
had any affinity with the fossils which have been described as 
belonging to the genus Ventriculites. This will be well under- 
stood by comparing PI. XIV. figs. 12 and 13 with any of the 
figures on PL XllI 
The condition in which these specimens are found, — their deep 
folds preventing their ever coming free from the chalk, or being 
developed without the laborious use of the needle, — renders it 
impossible to make any confident observations upon them as to 
the processes ; a remark which also applies to every other species 
of the present section. 
3. Cephalites constrictus. PI. XV. fig. 1. 
Whole body very low, much-elongated and narrow, with roots at 
one end : plaits very deep, and running longitudinally from the 
root extremity; each plait constricted at short and not very 
regular intervals, and sometimes to nearly its whole depth : 
cephalic membrane covering the whole upper surface and sides, 
to the margins of which last, as well as to many of the pro- 
minent points of the plaits, it is attached ; usually constricted 
at considerable intervals, with a single opening in the middle 
of each compartment thus caused. 
The specific description will satisfy the inquirer that this is a 
very extraordinary form. Externally it has nothing which would 
indicate any Ventriculitic affinity, and it has indeed been described 
by Dr. Mantell under the name of Choanites suhrotundus ; but it 
has no relation whatever to Choanites. The appearance of the 
fossils is so remarkable, that, but for the fixed rule of preserving 
every fragment which I could not understand, I should never 
have been able to establish or even suspect the true affinities. 
A suite of seventeen specimens enables me, however, now to point 
out the true general characters of the species without leaving 
any room even for doubt. 
In the two very different states in which the fossil, or frag- 
ments of it, are found, it has very different appearances ; the one 
state (see left hand of figure) shows the upper, the other (see 
right hand of figure) the lower part only, or its cast. The com- 
