73 



PLATE XXIX. 



Hymedesmia Zetlandica, Botverhcmk. 



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



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, ill situ. X 123 linear. 



Fig. 2. — One of the attenuato-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. 6. — A group of simple bihamate retentive 

 spicula. X 530 linear. 



Fig. 6. — A valve of Docinia exolita, having two 

 patches of the sponge on its inner sm-face 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. 

 Spongiadaa.' The large light-coloured patch opposite 

 n 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 XXVIII in 

 this volume. 



