17 



PLATE VIII. 



PACHTMATISMA JOHNSTONIA, Bowerbank, 



Vol. ii, p. 51, ' Mon. Brit. Spongiadse.' 



Fig. 1. Represents the type- specimen of P. Jolm- 

 stonia in the state in which it came from the sea, having 

 been preserved in spirit. Natural size. A portion of 

 the oscula are more or less open, while others are in a 

 closed condition. 



Figs. 2, 3. --Two of the numerous varieties of form 

 and size of the skeleton spicula. X 80 linear. 



Fig. 4. One of the connecting spicula. X 80 

 linear. These spicula are very variable in form and 

 proportions. 



Figs. 5, 6. -Two of the incipiently-spinous at- 

 tenuato-stellate, retentive spicula. X 250 linear. 

 Showing the variations in the size and number of their 

 radii. 



Fig. 7. A group of tuberculated fusiformi-cylin- 

 drical, retentive spicula. X 250 linear. 



This sponge afforded me a considerable number of 

 type forms of spicula to illustrate vol. i, treating on the 

 * Anatomy and Physiology of the Spongiadse.' I must, 

 therefore, refer the student to those figures for the 

 more complete illustration of the anatomy of this very 

 interesting specimen. 



Vol. i, plate xxvii, fig. 353, represents a section of 

 P. Johnstonia at right angles to the surface exhibiting 

 the irregularity of the skeleton structure directly 

 beneath the dermal crust. X 50 linear. 



In plate xxiv, figs. 330, 331, 332 in the same 

 volume there are figures of the ovaria ^in progressive 

 stages of development. 



