PLATE XXIX. 



HYMEDESMIA ZETLANDICA, Bowerbanfc. 



Vol. ii, p. 152, ' Mon. Brit. Spongiadse.' 



Fig. 1. Represents a portion of the sponge from the 

 specimen represented by fig. 6, exhibiting the fasci- 

 culated condition of the bi-clavated skeleton spicula, 

 and of the simple bihamate groups, and the rest of the 

 spicula, in situ. X 123 linear. 



Fig. 2. One of the atteuuato-acuate, entirely-spined 

 internal, defensive spicula. X 320 linear. 



Fig. 3. One of the tridentate, equi-anchorate, re- 

 tentive spicula. X 530 linear. 



Fig. 4. A bidentate, equianchorate, retentive spicu- 

 lum. X 530 linear. 



Fig. 5. A group of simple bihamate retentive 

 spicula. X 530 linear. 



Fig. 6. A valve of Docinict exolita, having two 

 patches of the sponge on its inner surface at a a. 

 There are also two small crania attached to the shell. 

 Natural size. 



Fig. 7. A small pebble nearly covered by the en- 

 crusting sponge represented by the lightest tinted 

 portion of the figure. Natural size. 



Fig. 8. Represents the specimen of Hymedesmia 

 radiata described in page 149, vol. ii, 'Mon. Brit. 

 Spongiadse.' The large light-coloured patch opposite 

 a being the sponge ; the smaller light-coloured patches 

 to the left hand in the specimen being calcareous. 

 Natural size. 



For the anatomical structures see Plate XXV1I1 in 

 this volume. 



