of the Ventriculidae 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 sonic 

 principal and most easily recognizable point in the ceconomy of 

 the living animal, and examining all the individuals under review 

 in reference to that one point. 



It has been already seen that the Ventriculidae 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 however 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 Ventriculidae ; 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 % 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. 



f Ante, vol. xx. p. 177-179. 



% A membrane, it will be remembered, which, by its structure, was firm 

 like the 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. 



