yiTROLLÜLA FERTILTS 41 



of the mass in contact with the substratum form a tliin close- 

 meshed limiting layer (see the lower part of fig. 22). 



The hypodenncdia (PI. ITT., fig. o) are moderately large 

 pentactins ; their rays closely resemhle in character those of 

 parenchymal hexactins. The regularly cruciate paratangentials 

 may measure 1 mm. in axial length and 27 // in breadth near 

 the spicular center. The proximal fifth ray is always longer 

 than the paratangential in the same spicule and at times is 

 nearly twice as long. Tn the smaller hypodermalia the size of 

 the paratangential cross approaches or may even nearly coin- 

 cide with that of the larger stauractinic dermalia, so that in 

 certain cases it is scarcely possible to decide whether a pentactin 

 is to be considered as a dermalia or a hypodermalia. This may 

 perhaps be regarded as an indication of the low degree of dif- 

 ferentiation of the species from the Leucopsacidae. Seen on sur- 

 face-view preparations, the paratangential crosses are situated for 

 the most part without any regularity of mutual arrangement, 

 though at places they may show an attempt, so to speak, at the 

 formation of a quadrate-meshed latticework. The hypodermalia 

 are never observed protruded as prostalia ; nor are they ever 

 found with shagreen-like surface. 



The dennaHa are stauractius, the plane of which is usually 

 slightly convex on the outer side. The rays are relatively long 

 and slender and gradually taper towards the conically or obtusely 

 pointed end ; the surface is roughened, generally all over, on 

 account of quite obsolete and insignificant microtubercles which are 

 scattered over it at rather wide intervals (PI. III., fig. 3). The 

 axial length fl^uctuates generally between 360 !'■ and 680 /z ; the 



