364 
Mr. Toulmin Smith on the Classification 
§ b. Aperti. 
Brachial folds open at extremity. 
1. Brachiolites foliaceus. PI. XVI. fig. 1. 
Membrane simple and without any primary fold : brachial fold 
variously winding and irregularly anastomosing, and thus 
forming irregular but close and connected sinuous cavities, with 
rounded, but irregularly arranged, external openings : mass 
rising to a considerable height ; expanding slowly from root, 
and the whole maintaining, throughout, a narrow diameter. 
The style of fold of this delicate species is very similar to that 
of the recent Eschar a foliacea. The form assumed by the whole 
mass differs how'ever materially. Instead of spreading horizon- 
tally, the habit of B. foliaceus was to rise perpendicularly. It 
sometimes attained six inches in height, but seldom more than 
an inch in width at its broadest part. The external openings in 
this species also differed materially ; those openings being usually 
separate, and circular or oval in form, not irregularly running 
into each other as in E. foliacea. 
Fragmentary portions in flint or chalk may readily be distin- 
guished from those of any preceding species by the greater deli- 
cacy of the membrane and closeness of the brachial fold. The 
upper part of fig. I. PI. XVI. shows the appearance displayed on 
a vertical section ; while the lower part of that figure shows the 
external appearance of the fossil when entire. 
The close anastomosing of the brachial folds of this species must 
have given great strength to the whole body ; while the freely 
communicating cavities would allow constant access and circula- 
tion of the sea-water. 
I have a specimen in which the whole animal part is converted 
into iron pyrites and the cavities are perfectly clear of all matrix. 
The species is found in Upper and Middle Chalk. 
2. Brachiolites racemosus. PI. XV. fig. 6. 
Membrane having a rather deep primary fold, round, and of 
nearly equal width the whole depth of the fold, and arranged 
in quincuncial figure : brachial fold beginning at some distance 
from the base, and running in narrow and short but regular 
cylinders ranged subspirally round a small central cavity at 
rather distant intervals. 
This species differs essentially from the last in having a deep 
])rimary fold ; in having a distinct central cavity, though varying 
in size, into which each of the brachial folds opens ; and in these 
