THE MOUNT DESERT REGION 113 



greatest breadth. The mode for the length of these spicules 

 is .203 mm.; (b) from the imier layer of the cortex. These 

 tylostyli are smaller but similar to those found in the skeletal 

 fibers, being strongly fusiform. They taper gradually to a 

 long fine point at one end, while the other end has the head so 

 feebly developed as to barely justify classing them as tylo- 

 styli. They rather more resemble styli with a slight and 

 indefinite constriction. These spicules vary from .405 to .526 

 mm. in length and from .0075 to .0094 mm. in breadth. There 

 is no modal length for these spicules except there are fewer 

 of the extremes. 2) Tylostyli from the skeletal fibers. These 

 spicules are strongly fusiform as well as being similar in all 

 other respects, except size, to those from the inner layer of 

 the cortex. These spicules vary fom 1.087 to 1.5 mm. in 

 length and from .018 to .022 mm. in breadth. 



Remarks. This species resembles P. laganoides Lambe 

 (1895, p. 129, pi. 4, figs. 5, 5a-c) in certain features. However, 

 the distribution of the various classes of spicules within the 

 sponge is quite different. In P. laganoides the spicules of the 

 dermal layer do not belong to the smallest class, whereas in 

 this form they do. It is barely possible that Lambe may 

 have been mistaken in this, for in most Polymastia the dermal 

 layer contains the smallest spicules found in the sponge. He 

 calls attention to the fact that in this sponge there is the 

 '' absence of a regular radiating arrangement of the spicules 

 of the cortex; the spicules are closely intermixed and lie at 

 all angles to the surface, those that project beyond it causing 

 a slight hispidity. " This description fits rather well for the 

 inner layer of the cortex and is unusual for the dermal layer 

 in this genus. As Lambe described this species from a single 

 specimen it may be that in this case the dermal layer has 

 been injured and partially destroyed. His description of the 

 surface and oscula also suggests this possibility. Such other 

 minor differences as exist between them might well come 

 within the limits of variation when more material is studied. 



Geographical distribution. Mount Desert Region ; probably 

 some of the Polymastia sp. ? of Verrill's lists may be identical 

 with this form. 



