of the Yentriculida? of the Chalk. 
3G9 
7. Brachiolites protensus. PI. XVI. fig. 5. 
Membrane having a slight and irregular primary fold : brachial 
fold in large sinuous tubular masses frequently anastomosing 
and opening into each other^ and with occasional, but irre- 
gular, large interstices : mass very irregular and usually spread- 
ing horizontally. 
This species will perhaps be best understood if the inquirer 
conceives a number of the arms of B. digitatus to be more or 
less contorted instead of straight, and to anastomose and open 
into each other instead of always being distinct from each other 
at all other points than their bases. The tubular folds of B.pro- 
project from the mass not very prominently, but still con- 
spicuously and in every direction. The primary fold differs how- 
ever, as will be seen both by the description and figure, most 
essentially from that of B. digitatus. 
The habit of the mass is the very reverse of being compact like 
B. labrosus ; it ma}'’ best be described as sprawling, whence the 
name; its tendency being usually to horizontal rather than 
perpendicular extension : it does not seem to have any inclina- 
tion to assume the globose or any other definite general figure. 
The mouths of the tubes tend to expand as in B. labrosus, while 
in B. digitatus their tendency, where not simply straight, is rather 
to contract as in B. tubulatus. 
This species is from the Low'er Chalk and Chalk Marl, 
I have thus laid before the reader the result of an investiga- 
tion which has engaged most of the leisure hours of some years. 
I am too conscious of the disadvantages under which 1 labour, 
and the want of qualifications which I possess, to anticipate 
otherwise than much criticism as to the result of that investiga- 
tion and the execution of my task. I would only request the 
reader to remember that the field was an entirely untrodden one 
and the task a new one, — ^^a task of no little difficulty in the ac- 
complishment, and one that may fairly entitle him who enters 
upon it to expect to meet with indulgence 
I have endeavoured to show the existence, in one, at least, of 
the great geological epochs, of a widely extended class of animals 
whose nature, — if the existence of a few of the forms was vaguely 
known before, — was totally unknown, as also was their structure 
and all that constitutes the knowledge of an organic being. I 
have exhibited a structure as remarkable as it is novel. I have 
shown the extraordinary variety of forms which that structure 
assumes, — a variety in which one Law of Unity, however, still 
* Favre, iit ante, p. .‘t87. 
Ann. Mag. N. Hist. Ser. 2. Vol. i. 
25 
