FROM THE YORKSHIRE CHALK. 11 



The kind most abundant near Bridlington is the Spongia 

 radiciformis of Phillips ; numbers of this species lie in all 

 directions in the cliff below Sewerby, both parallel with, and 

 across the direction of the strata : many specimens appear 

 to have been a good deal worn before they were imbedded, 

 while others, particularly of the cup-shaped form, are per- 

 fect, even to the finest fibres of the root. In some cases 

 these latter have disappeared, but are yet shown very beau- 

 tifully by the hollows in the chalk they once filled, being 

 coloured with ochreous matter. 



I have never yet observed the root of any sponge attached 

 to any of the other fossil bodies which are found in the chalk; 

 this fact appears singular, since the fine fibres of the root 

 are in many cases perfectly preserved: about two years 

 ago however, I obtained a specimen of a variety of Spon- 

 gia radiciformis, (or perhaps a new species), in which the 

 short thick fibres of the root appear attached to the head of 

 another individual of the same species. 



The variety in outward form has been already referred to ; 

 the internal structure also exhibits very great irregularity of 

 character : for instance, it has been generally believed that 

 the root-shaped sponges had a central cylindrical cavity, ex- 

 tending downwards to the stem : the annexed diagram (fig. 1.) 

 jtnpn^ shows however that this character is not con- 

 stant: it is a magnified representation of the sec- 

 tion of one of these fossil bodies. The specimen, 

 when obtained, was broken in two or three places ; 

 in the lower part of the stem there was a simple 

 circular perforation, but about an inch higher this cavity 

 had assumed a quadrangular appearance, and other circular 

 canals were visible on each side, two of which were of much 

 larger size than the others. At first sight, it appeared to con- 

 nect the Siphonice with the Choanites of Mantell, and being 

 very anxious to obtain further specimens, I examined with 

 great care the neighbourhood of the spot where this fossil 

 was procured : from that day to this however, I have never 

 been able to find another instance of such a conformation, 

 and at length I have come to the conclusion, that these cha- 

 racters must be considered as merely accidental. 



The young Spongia are very abundant along the whole 

 face of the cliff : a great variety of globular specimens may 

 be obtained, from the size of a small pea to that of a common 

 nut; the form then becomes rather conical, and there are 

 often appearances of a process of attachment. — As they in- 

 crease in size the specific characters gradually develope them- 



