of the Ventriculidse of the Chalk. 355 



latus, as to observations upon the processes, applies equally to 



every species of the present genus. Enough, however, can be 

 detected to determine the fact of their presence. 



This species must, in its recent state, have been singularly 

 striking. It is difficult, indeed, to conceive anything more beau- 

 tiful than must have been its exterior with each of its regularly 

 ranged lobes covered with its myriads of living polyps and their 

 ever-active tentacles. 



All my specimens are from the Upper Chalk. 



2. Brachiolites elegans. PI. XV. fig. 4. 



Membrane simple and without any primary fold : brachial fold 

 beginning almost at the acute base, and rapidly increasing in 

 broad and swelling lobes closely arranged round a central ca- 

 vity, and terminating in a simple and regular crown, open at 

 the top, and which, rising from the midst, reaches to a consi- 

 derable distance above the highest lobes, and is of about half 

 the diameter of the whole body. 



This form is, in its fossil state, frequently so beautiful that I 

 have hence chosen its specific name. The effect is heightened 

 by the fact that the root of this species is usually long, and often 

 maintains the same diameter for a height of nearly two inches. 



The primary membrane is exactly similar to that of Ventri- 

 culites simplex : the brachial folds are deep and broad, their inner 

 surface being freely exposed to access of sea-water from the large 

 internal cavity. The crown is one of the most remarkable fea- 

 tures of this species. It is regular and plain ; springs from the 

 lower edge of the most deeply folded lobes, and rises, unbroken, 

 to a clear and even margin. A glance at fig. H, p. 291, illus- 

 trative of the fold of Cephalites campanulatus, will aid in un- 

 derstanding the anatomy of the present species ; broad convolu- 

 tions here replacing the plaits seen in that specimen, and the 

 crown being always straight-sided, and never, I believe, assuming 

 a funnel form. Nothing can show more convincingly than this. 

 peculiar crown, that the forms of the Ventriculitis are not 

 merely arbitrary massings of an amorphous or simply cumulative 

 organism, or mere examples of " vegetative repetition," but that 

 there was a type appointed to each which it should attain, and 

 each having its special adaptations. In perfect specimens this 

 head is never wanting, though it is rarely, if ever, to be seen 

 without the aid of the knife ; whence it is that it has never, so 

 far as I am aware, been heretofore observed. 



The species appears to be characteristic of the Upper Chalk. 



3. Brachiolites convolulus. PI. XV. fig. 5. 



Membrane coarse in texture, simple and without any primary 



24* 



