284 Mr. Toulmin Smith on the Classification 
5. Cephalites hullatus. PI. VII. (vol. xx.) fig. 3, & PI. XIV- 
figs. 6 & 7. 
Plaits broad and deep : outer plaits raised in large and very pro- 
minent projeetions at considerable intervals^ and in such man- 
ner that they range spirally round the whole body : projections 
nearly lozenge-shaped and terminating abruptly in an almost 
flat and somewhat expanded top, having a slight depression from 
the upper angle towards the middle : inner plaits having large 
circular depressions at equal intervals ; bulging on each side 
around depressions till adjoining plaits meet and open into 
each other : processes very conspicuous : wall very thick. 
This is a most curious and interesting as well as rare but well- 
marked species. The depressions on the inner folds are much 
larger than in C. guttatus, which latter have been seen to be 
larger than in C. longitudinalis. But the external fold is the 
most deserving of attention. When the specimen is first opened 
there are seen only a number of nearly semilunar marks. On 
carefully applying the point of the knife it is found that this se- 
milunar appearance is caused by very prominent projections, the 
tops of which are all closed, but have a partial depression at their 
upper extremity, and which depression is filled as usual with the 
matrix. The projections themselves are of large size, measuring 
about two lines in their longest diameter. They stand out nearly 
or quite half the thickness of the wall, which is generally four 
lines thick (see fig. 3. PL VII.*). They differ widely from any- 
thing we have yet seen. Instead, like Ventriculites mammillaris, 
of being mere rounded elevations on the plait, they stand out 
prominently from it ; and a careful dissection shows that their 
shape is generally that of a lozenge, with the acute angles in the 
horizontal, and the obtuse in the perpendicular, line of the whole 
body. Fig. 7f of PI. XIV. shows the manner of the projections 
from the plait and the figure which the peculiar shape of their 
tops causes to be seen on a clean section exactly through the 
middle of any one. In all the specimens of this species w^hich I 
have seen, the projections run in nearly regular spiral lines round 
the body. 
On the inner surface of this and of some other broadly de- 
pressed species there is a very small and slight depression be- 
tween each of the large depressions, and both on the plaits and 
on the places of the united bulgings. It is barely traceable, and 
* This is a longitudinal section taken rather obliqueb- in order to preserve 
the roots. It is not quite regular therefore; but, on the side which is pre- 
served, the projections can be well distinguished. 
f In this figure I have connected the inner and outer plaits by brackets, 
— the outline of each merely being given for the sake of clearness. 
