282 Mr. Toulmiii Smith on the Classification 
that a section of the entire body presents an 
outline as in fig. V, in which a — b is the sec- 
tion of the head. The outline of the head 
is always quite as sharp and well-defined as 
in this figure. The relative arrangement 
and proportions of the head and the plaits 
are such that specimens of this division can 
never be confounded with any belonging to 
the section Dilatati. It is very rarely in the 
present division that there is any rounding, 
or departure from the nearly flat character of 
the head; a character, on the other hand, 
never present in the Dilatati. 
It is proper to notice that, in every species of this genus, in 
order to give full strength to the head, the depressions, bulgings, 
and other modifications of the fold, — where it does not rise, as 
in C. campanulatus, in a simple form, — are so arranged that the 
membrane of the inner wall, where it adjoins the head, is always, 
and that of the outer wall most frequently, expanded by a lateral 
bulging of the plait, so as for the adjoining plaits to meet just 
at the point of union of the wall wdth the head. Thus the 
whole of the inner, and often of the outer, edge of the head is 
continuously attached to the wall, an arrangement of much im- 
portance. On this inner edge the membrane often rises up in a 
narrow and slightly prominent ridge above the otherwise smooth 
surface of the head. 
2. Cephalites guttatus. PI. XIV. fig. 2. 
Plaits broad and deep : outer plaits raised in large hollow bosses, 
often elongated ; adjoining plaits having an occasional lateral 
connection : inner plaits depressed at regular intervals, bulging 
on each side around depressions till adjoining plaits meet and 
open into each other : processes very conspicuous : wall usu- 
ally thick. 
Nothing can better express the usual character of this species 
than the term guttatus. The outer surface looks exactly as if 
sprinkled with drops of a viscid fluid which had just begun to 
run together, in some instances to a greater, in others to a less 
extent. It is thus generally well distinguishable, even on the 
outside, from Ventriculites mammillaris. The plaits being much 
broader than in C. longitudinalis, the depressions on the inner 
plaits are larger than in that species. 
The lateral connection between adjoining external plaits, as in 
Ventriculites latiplicatus and radiatuSj which is only rarely seen 
in C. longitudinalis, is always more or less present in this species. 
Fig. F. 
