17 



PLATE VIII. 



Pachtmatlsma .loiiNSTONiA, Boioerhanh. 



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



Fig. ]. — Represents the type-specimen of P. John- 

 stonla in the state in wliicli it came from the sea, having 

 been j^reserved in spirit. Natural size. A portion of 

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

 closed condition. 



Figs. 2, 3. — Two of the nnmerous 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 numbei' of their 

 ■ radii. 



Fig. 7. — A group of tuberculated fusiformi-cjdin- 

 drical, retentive spicula. X 250 linear. 



This sponge afibrded me a considerable numljer of 

 type forms of spicula to illustrate vol. i, ti'eating on the 

 ' Anatomy and Physiology of the Spongiada^.' 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 rio'ht angles to the surface exhibitins; 

 the irregularity of the skeleton struetui'e directly 

 beneath the dermal crust. X 50 linear. 



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

 vohime tliere are figures of the ovaria in progressive 

 stages of development. 



