THE MOUNT DESERT REGION 107 



short, irregular, often strap-shaped, papillae clustered within 

 a depression. This opening is circular or ovoid in shape and 

 about 6 mm. in diameter ; the details of this region are often 

 obscured by the quantities of mud and sand which usually 

 adheres to the surfaces of the specimens. The true oscula are 

 to be found, it is suspected, at the tips of the papillae. In 

 small specimens there is present usually only a single oscular 

 area, but in large individuals as many as 5 or 6 may be pres- 

 ent. Lambe states that "at the margin of the osculum [= 

 oscular area] the projecting tylostyli are directed toward a 

 point a little above the opening." Such is the case in most 

 of the specimens from this region, and this condition is 

 another factor which helps to obscure the true nature of this 

 area. 



Skeleton. This is composed of loose fibers which pass from 

 the base to the surface of the sponge. In the cortex, two sizes 

 of tylostyli are present. The small tylostyli, radiating out- 

 ward, are densely packed together and project slightly 

 beyond the surface. The inner cortical layer contains larger 

 tylostyli which are loosely and irregularly placed. Long cor- 

 tical tylostyli, similar to those in the main fibers, project 

 beyond the surface. At the margins of the oscular areas 

 projecting tylostyli are frequently found directed toward a 

 point a little above the center of this area. 



Spicules. 1) Stout, fusiform, gradually tapering and finely 

 pointed tylostyli with feebly developed heads form the skeletal 

 fibers. These vary in length from 1.08 mm. to 1.64 mm. 

 2) Stout, slightly bent, sharply pointed tylostyli with well- 

 marked heads compose the inner layer of the cortex. They 

 range from .324 mm. to .526 mm. in length. 3) Small, usually 

 curved, sharply pointed tylostyli with well-developed heads 

 are very abundant in the dermal layer of the cortex. These 

 vary from .121 mm. to .203 mm. in length. 4) Very long, 

 sharply pointed tylostyli with well-developed heads project 

 far beyond the surface of the sponge and give it a very hispid 

 surface. These spicules vary from 2.47 mm. to 3.28 mm. in 

 length. 



