190 PLATE LXX1L 



face, and the large attenuato-triradiate spicula are 

 also few in number. They are remarkable for the 

 frequent contortions of their radii ; a few of them are 

 spiculated, the spicular ray most frequently passing 

 outward. The inflato-acerate spicula are by far the 

 most abundant of the tension ones, and in some parts 

 they are thickly felted together, especially around the 

 areas of the pores. These spicula are singular in 

 their structure, and are very characteristic of the 

 species. They are very variable in their characters; 

 the central inflation is well produced in some, while in 

 others it is scarcely visible or entirely absent; the 

 incipient tuberculation is also variable ; in many 

 of them, it has the appearance of hemispherical nodules, 

 while in others it is so slightly produced as to assume 

 the form of a very early stage of incipient spination, 

 and in all of them it is more or less apparent on every 

 part of the spiculum when viewed with a power of 

 about 800 linear. The attenuato-elongate stellate 

 retentive spicula are also abundantly dispersed on all 

 the membranes, and especially so on the inner surface 

 of the dermal one. They are minute, variable in size, 

 and very irregular in form, requiring a power of about 

 800 linear to demonstrate them in a satisfactory 

 manner. 



The structure of the skeleton is open and diffused, 

 and occasionally a few of the spicula are fasciculated, 

 but these fasciculi are not continuous for more than 

 twice or thrice the length of a spiculum. The tension 

 and retentive spicula of the interstitial membranes are 

 not quite so abundant as in the dermal membrane. 

 The interstitial membranes are so thin and pellucid 

 that they would scarcely be visible if it were not for 

 the numerous spicula they contain. 



The colour and general aspect of the sponge in its 

 dried condition is so like many flat and imperfect 

 specimens of Plialicllia ventilabrum that it might 

 readily be mistaken for one of that species when mixed 

 with them. 



