PLATE XXXIV. 



Figs. I, 1 a. Tremacystia D'Orbignyi, Hinde. Natural size. From the Upper Green Sand 



at Warminster, Wiltshire 272 



Fig. 1 b. The same. A portion of the outer surface of the wall, enlarged thirty times, 

 showing the circular canal-apertures and some of the large four-rayed spicules 

 forming the dermal layer. 



Figs. 1 c-1 k. The same. Detached sagittal three- and four-rayed spicules belonging to the 

 dermal layer. Enlarged seventy-two times. 



Figs. 1 /, 1 m. The same. Detached three-rayed spicules of the fibre. Enlarged seventy- 

 two times. Fig. 1 Z is a comparatively rare form, whilst the spicules represented 

 by 1 m form the main components of the fibre ; in these the third ray is only 

 represented by a minute process. 



Figs. 1 n, 1 0. The same. Two three-rayed spicules of the fibre. Enlarged two hundred 

 times. In 1 the sagittal rays are curved, whilst in 1 w they are straight. 



Fig. 2. Tremacystia siphonioides, Mich. sp. A group of individuals growing on a common 



expanded base. Natural size. From the Upper Green Sand at Warminster . 173 



Fig. 3. Tremacystia cribrosa, Goldf. sp. The upper portion of an individual. Natural 



size. From the Cenomanian at Essen, Rhenish Prussia 174 



Fig. 3 a. The same. Enlarged twice the natural size. In the upper portion of the speci- 

 men the outer wall is broken away, and the interior cyst-like chambers, each 

 with a circular aperture opening into the central tube, are exposed. 



Fig. 3 b. The same. The fractured under surface of the same specimen, seen from below, 

 enlarged twice, showing the central tube and the chambers surrounding it. 



Fig. 4. Tremacystia anastomans, Mant. sp. Natural size. From the Lower Green Sand 



at Farringdon, Berkshire 175 



Fig. 4 a. The same. A portion of the outer surface of the wall, enlarged thirty times, 

 showing the irregular canal-apertures. 



Fig. 4 b. The same. A fragment of an individual spongite, with the outer wall broken away, 

 showing the chambers with horizontal partitions, and the central tube with the 

 apertures communicating with each chamber. Natural size. 



Fig. 4 c. The same. The summit of one of the spongites. Natural size. 



Fig. 5. Tremacystia irregularis, Hinde. Natural size. The outer wall of some of the 

 spongites is .broken away, and the arched and irregular form of the partitions 

 of the chambers is exposed 175 



Fig. 6. Tremacystia clavata, Keeping, sp. A small simple individual. Natural size. At 

 the summit is seen the oblique eliiiJtical aperture of the central cloacal tube, 

 and immediately below, the outer wall is broken away and two of the chambers 

 are exposed 1/6 



Fig. 7. Elasmoccelia Furring donensis, Mant. sp. Natural size. From the Lower Green 



Sand at Farringdon 177 



Fig. 7 a. The same. A portion of the interior fibre, enlarged seventy-two times, showing 



