Spongida from New Brunswick. 87 



each being pervious throughout and without tabular Each 

 is in relation with those on all sides of it by means of regular 

 three-, four-, or six-sided spaces in its walls. The canals are 

 subequal ; but here and there some are larger than the others. 

 They arise from the central space, bifurcate occasionally, thus 

 increasing in number, and end at the surface in the areas be- 

 tween the nodules and reticulation seen there. The largest 

 canals measure y 1 - inch in diameter, and the smallest about 

 Totj of an inch. Their length varies with the size of the 

 specimen ; for they constitute the larger part of the fossil. 



They are more or less hexagonal or quadrangular in sec- 

 tion, and are filled with the minerals already noticed. They 

 were patent throughout before fossilization took place, and 

 neither cross pieces, tabuhe, nor septa encroached on them ; but 

 it should be noticed that under a hand-lens tabulate structures 

 appear very evident here and there ; but they are resolved into 

 parts of overhanging canal-walls under the compound micro- 

 scope and careful focusing. 



The canal-walls and their reticulation, as well as that on the 

 outside, which is the expression of the outermost skeletal 

 element of the canals, and the reticulation of the central part, 

 are composed of similar structures, which are closely united 

 in the first, and less so or separate in the last place. 



The union of the spicules (for such are the skeletal elements) 

 is often so intimate that the canal-walls appear to be con- 

 tinuous. But in thin sections, and in certain places in others, 

 the skeleton resolves itself into numerous combinations of 

 spicules closely resembling those of the Tetraclade Lithistidas 

 in shape and method of junction. 



These canal-wall spicules resemble those which are free or 

 nearly so in the central space. In no instance, however, has 

 a central canal, or a canal in the three or four arms of a spicule, 

 been observed. 



Typical spicules, from the central space, consist of three 

 arms in one plane uniting at a common point, from which 

 another arm may spring and be in a plane at right angles, 

 more or less, to the others. These tripod-stemmed spicules 

 are often ragged or papillate on one or more surfaces, appear 

 solid under the microscope, and are often compressed. They 

 differ in size, and are usually the largest in the outer parts of 

 the central space, where the canal-system is commencing. The 

 simplest form of spicules has two straight or slightly curved 

 arms, which are widely apart, forming an angle of 35° to 45° 

 where they meet and join a smaller and shorter third, which 

 lies in a different plane. The larger arms are flattish ; and 

 their opposed surfaces (sometimes the others) arc nodular or 



