of the Ventriculidse of the Chalk. 41 
terial points of likeness or unlikeness which should mark separate 
species*. 
The only principle upon which I can understand any philoso- 
phical or natural classification to be founded, is the taking some 
principal and most easily recognizable point in the oeconomy of 
the living animal, and examining all the individuals under review 
in reference to that one point. 
It has been already seen that the Ventriculidse belong to a 
high type of the Molluscan Polyps, — to the Polyzoa, — approach- 
ing most nearly to the recent Eschara and Halodactylus. The 
fossilized remains of animals of this order, the organization of 
whose recent congeners has been but so lately understood, might 
seem at first sight to baffle any attempt to seize on such a point. 
It seems to me hov^ever that such a one may be found. In all 
recent animals of this order the first essential to their life and 
well-being is the presence and free access of the sea- water. Va- 
rious contrivances are adopted to secure this end, — some genera 
and species being parasitical, some loosely floating, some stiffly 
erect ; each, varying as they also do in form, adapted to the pe- 
culiar circumstances of the locality which it inhabits, and each, 
according to the particular plan adopted, exhibiting some charac- 
teristic differences in habit and organs. This is precisely consistent 
with the observations already madef as to the constant relation 
existing between the polypidom, rightly examined, and the nature 
of the inhabiting polyps. Such differences no doubt existed in the 
recent Ventriculidse; and though it is obviously impossible that 
we should ever be able, in these fossils, to ascertain the points of 
difference in habits and individual organs, we may, by care and 
patience, ascertain those differences in the contrivances displayed 
in the structure of the polypidoms which we must thus be satis- 
fied were intimately and necessarily connected with such differ- 
ences in habits and individual organs. I allude to the various 
modes of folding of the delicate membrane J which forms the 
framework of every individual of this family, and on whose sur- 
face the minute and numberless colony of polyps dwelt. I ap- 
* Were I to follow the example of some botanists, who, for example, in 
a favourite tribe, the Cactus, have amused themselves with hair-splitting of 
genera to a marvellous extent, I might readily succeed in perplexing the 
inquirer with a great multitude of unintelligible names. Between many 
of the species which I have grouped together, differences far more marked 
exist than those by which these gentlemen — and too many palaeontologists 
— have overlaid the intelligibility of their classifications as generic distinc- 
tions. 
t vol. XX. p. 177-I79. 
+ A membrane, it will be remembered, which, by its structure, was firm 
like Eschara (though not calcareous), and not loosely floating like the 
Halodactylus. This is important in considering the permanence of the 
different modes of folding adopted. 
