THE MOUNT DESERT REGION 111 



Spicules: 1) Cortical tylostyli (a) from the dermal layer 

 of the cortex. These tylostyli are small, usually rather 

 strongly curved, slightly fusiform with well-developed heads. 

 They vary in length from .061 to .218 mm., with the mode at 

 .186 to .20 mm. ; (b) from the inner layer of the cortex. These 

 tylostyli are similar to those found in the skeletal fibers. 

 They vary in length from .445 to .688 mm. and in breadth 

 from .008 to .012 mm. These spicules have feebly developed 

 heads and are sometimes rather abruptly curved near the 

 head end. 2) Tylostyli from the skeletal fibers. These 

 tylostyli have such feebly developed heads as hardly to jus- 

 tify calling them tylostyli. 



These spicules are slightly fusiform, tapering gradually 

 to a long sharp point at one end and tapering slightly toward 

 the head, which is almost imperceptibly inflated. These spic- 

 ules vary in length from 1.08 to 1.36 mm. and in breadth from 

 .016 to .024 mm. This type and the preceding show no definite 

 modal length. 



Remarks. Lambe records only two sizes of spicules : those 

 from the cortex and the skeletal fibers. However, he adds 

 that "spicules similar in size and form to those of the main 

 fibers of the body of the sponge occur in some numbers be- 

 neath the cortex, [= inner cortical layer] parallel to the sur- 

 face." The measurement given by him for the small cortical 

 tylostyli agrees very well with those from our specimen. The 

 sizes given by Lambe for the 'large tylostyli of the body' 

 embrace those given here for both the spicules of the inner 

 cortical layer and the skeletal fibers. However, there is a 

 discontinuity in size in our specimen as well as a slight struc- 

 tural difference noted above, but there is little doubt of the 

 identity of the two forms. 



Geographical distribution. Gulf of St. Lawrence (Lambe), 

 Portland, Maine (Sir William Dawson); off Halifax ('Chal- 

 lenger'), northeast coast of United States (Verrill), Mount 

 Desert Eegion. 



