359 
of the Ventriculidse of the Chalk. 
is seen in the accompanying 
figure. This can, in itself, 
give little idea of the form or 
nature of the recent animal. 
I have a specimen of this 
aspect nine inches across. 
Anxious to ascertain the true 
natm’e of this remarkable ap- 
pearance, of which no expla- 
nation had ever been even 
offered, I carefully collected 
every fragment I could find, 
until I was led to infer a rela- 
tion between certain flat and 
unconnected surfaces, some • 
times found, and these mark- 
ings. I was fortunate at 
length in obtaining two specimens, each of very large size, and 
which exhibited on one end the aspect of fig. P, and on the broad 
side, and in continuous connexion with one of the lines of that 
peculiar marking, an entire and unbroken surface of many square 
inches in extent. It became obvious that the inference already 
made had* been correct*; that these markings were caused by 
the transverse section of a membrane very deeply folded up. I 
then had recourse, as in other cases, to dissection, in order to 
ascertain the entire form and habit of the creature, which no 
specimen developed in the ordinary way could ever show. The 
extreme fineness of the membrane, and the great depth of the 
brachial fold, made the task a very difficult one. Having, how- 
ever, succeeded in several instances, I have been able to restore, 
from specimens thus cleared out, the beautiful and extraordinary 
form seen in figure 0, a form of animal life seldom if ever exceeded 
in beauty and striking evidence of design and adaptationfi. 
The Vv^all of this species is exceedingly thin and delicate, the 
* These specimens had been shown by me to several friends, and my in- 
ference of the habit of the animal, with a model in paper of what I con- 
ceived its form to be, explained to them long before the importation of the 
11th livraison of Michelin’s ‘ Iconographie Zoophytologique ’ (see ante, 
p. 80). Plate 30 of that work became an interesting illusWation of the pre- 
sent species, though giving little idea of its true character, and none what- 
ever of its habit, on neither of which points do the accompanying descrip- 
tions atford any real aid. The character of the surface is there very imper- 
fectly represented, and the magnified views are not truthful, which they 
could hardly be since that author had no idea of the true structure of this 
class of fossils. 
t This figure, as well as all the other woodcuts illustrative of the present 
subject, has been executed, with great care and faithfulness, by Mr. Frederick 
Gyde. 
Fig. P. 
