224 ART. 7. — I. uni A : hexactinelltda, iv. 



form over the dermal surface a gossamer-like covering, which in 

 places is about 5 mm. thick. They generally protrude in groups 

 of two or more but may sometimes stand out singly. 



The dermalia, together wdth the hypodermal spicular rays, 

 form quite an irregularly meshed latticework. The meshes are 

 never quadrate but triangular, trapezoidal or indefinite in shape. 

 This irregularity has its explanation in the fact that the dermalia 

 are predominantly straight diactins, wdiich may lie in all possible 

 directions in the plane of the dermal layer (PL XVI., fig. 15). 



The subdermal space is inconspicuously developed. The 

 variously sized apertures of incurrent canals are largest in the 

 broadest region of the body. Here they occasionally measure 3 

 or 4 mm. across. Apertures of a similar size are separated from 

 one another by a space as wide as, or wider than, their own 

 width. 



The gastral surface presents a loosely felt-like appearance, 

 not being covered with a well differentiated endosomal layer (PI. 

 XVI., fig. 1). On it the excurrent canals, up to o mm. in width, 

 open with free apertures. These canals are mostly not deep but 

 are seen soon to divide up into branches. 



Spiculation. 



The larger parenchymalia, which may be called the princi- 

 palia, are elongate spindle-shaped oxydiactins, either nearly straight 

 or gently bent in a bow-like manner. They may attain dimen- 

 sions of 7 nun. length and 80 /^ breadth at the middle. The ends 

 are usually rough in varying degrees ; in other cases they are 

 smooth. Under certain circumstances, one end of the diactins 



