302 DR. J. S. BOWERBANK ON THE SPONGIAD^E. [May 5, 



fig. 2, Plate XLVIL, is very regularly cup-shaped, but with the addi- 

 tion of a small fan-shaped offset from its base ; and in a third cup- 

 shaped one in my possession numerous thin fan-shaped ridges are 

 projected from the outer surface, some of which are more than half 

 an inch in height : and I have had several fan-shaped ones of very 

 considerable dimensions : one in my possession is very little short of 

 14 inches in breadth ; and many years since I gave a still larger one 

 to the British Museum. A remarkable circumstance, which seems to 

 prevail in the cup-shaped specimens, is that they all appear to have 

 an orifice near the bottom of the cup, as represented in fig. 1, Plate 

 XLVII. ; but it does not always exhibit the same regularity ; in the 

 specimen represented by fig. 2, it is much larger and more irregular 

 in form. The ridged or mammillated surface-structure is the same 

 in every form or size of the species. 



The dermal rete is a strong closely constructed network, so laden 

 with particles of sand that the keratose-fibres are rarely to be 

 distinctly seen. The oscula are situated on the mammae or ridges of 

 the exhalant or inner surface of the cup, and they are so minute as 

 to be scarcely visible without the aid of a 2-inch lens. 



The primary fibres of the skeleton are mostly disposed at right 

 angles to the outer and inner surfaces of the sponge, and each fibre 

 has usually a single closely packed series of arenaceous particles of 

 nearly equal size ; and the distal fibres of the skeleton may be fre- 

 quently seen projected beyond the outer surface, each terminated 

 with a single molecule of sand encased in a thin coat of transparent 

 keratode. The secondary or internal connecting fibres are mostly 

 destitute of arenaceous matters ; a few short lengths of broken 

 sponge-spicula are occasionally found embedded in them ; their 

 general line of disposition is at right angles to the primary fibres. 



This species is especially interesting as exhibiting a very close 

 alliance with Dr. Man tell' s fossil species of Ventriculites radiatus, 

 described and published in his work on the Geology of Sussex, 

 p. 468, and figured in tables x., xi., xii., xiii., & xiv. of that work. 

 The author instituted the genus Ventriculites for the reception of 

 a series of fossil forms which were considered by him to be silicified 

 Alcyonia; and in p. 168 he gives the following as its generic and 

 specific characters : — 



" Generic character. — Body inversely conical, concave, capable of 

 contraction and expansion ; original substance spongious (?) or gela- 

 tinous (?), external surface reticulated ; internal surface covered with 

 openings or perforated papillae ; base imperforated, prolonged into a 

 stirps, and attached to other bodies. 



"Specific character. — Infundibuliform ; external integument com- 

 posed of cylindrical, anastomosing fibres, radiating from the centre 

 to the circumference ; inner surface covered with perforated papillae 

 formed by the open extremities of short transverse tubuli ; stirps 

 fixed by radical processes." 



The learned author accounts for the great variety of forms 

 assumed by these animals as "partly attributable to the various forms 

 of expansion and contraction in which the originals were introduced 



