36 DAWSON AND HINDB 



Dictijophyton, Hall, ustially retain their outer forms complete — that is, without beiug 

 compressed — but most of these sponges exhibit only internal casts of their spicular 

 skeleton, so that at present we know very little of their original structures. 



" As already mentioned, nearly all these Quebec sponges belong to the suborder of 

 the Hexactinellidse, in which the fundamental type or elementary spicixle of the skeleton 

 consists of six equal rays, radiating from a common centre at right angles to each other, 

 forming three equal axes. But this typical form is subject to great modifications through 

 the unequal development or even suppression of one or more of the individual rays, so 

 that spicules with five, four, three, or merely two rays only, are frequently present, and 

 in the same species of sponge several modified forms of spicules may be found. Now, 

 in the compressed condition in which the Quebec sponges occur, we can, as a rule, 

 only perceive those rays of the spicules which lie in the exposed plane of the rock ; these 

 are generally the four transverse rays of the normal spicu.le, but the two rays forming the 

 axis at right angles to the transverse rays, are not likely to be distinguished, for one 

 would be concealed in the matrix immediately beneath the transverse rays, whilst the 

 other, projecting above the exposed surface, would inevitably be broken away. Conse- 

 quently it is very difficult to determine positively whether the forms with four transverse 

 rays exposed on the plane of the sponge-wall, represent the entire spicule — in which 

 case it would be termed cruciform, — or whether one or both of the other rays of the 

 normal spicules were originally present. Judging by the analogy of allied recent forms, 

 it is probable that in most cases these spicules were furnished with a fifth ray at right 

 angles to the other four. In the examples of Oyathophycus from the Utica shale, are 

 distinct traces of a fifth ray in some of the larger spicules, and it can also be seen in 

 detached spicules from the Quebec group. 



" In both recent and fossil hexactinellids, many of the elongated filiform anchoring 

 spicules terminate distinctly in four short recurved rays, and are thus five-rayed spicules 

 in which one ray is greatly developed ; but in other instances they have simple blunt or 

 pointed ends, and may thus represent only one ray or one axis of the normal spicule. 

 With the exception of two species, all the anchoring spicules present in the Quebec 

 sponges seem to be merely pointed at their distal ends. In one species they are complex, 

 consisting of several filaments twisted spirally. 



" In recent hexactinellid sponges, in addition to the spicules forming the regular 

 framework of the skeleton, there are much smaller spicules of varied forms, imbedded in 

 the soft tissues. These, generally known as flesh-spicules, are very seldom met with in 

 the fossil condition, but it is not improbable that the delicate film of pyrites, seen in 

 places on the .surface of the Quebec sponges, may arise from the replacement of the flesh- 

 spicules by this mineral." 



The species of sponges noticed below have been submitted to Dr. Hinde, author 

 of the British Museum, " Catalogue of Fossil Sponges," and the following descriptions 

 are largely based on his notes on the specimens. The magnified tracings of the 

 structures in the text have usually been drawn under the camera to one scale (about 

 five times the natural size). The restorations are based on comparison of the more 

 perfect specimens, some of which are represented from photographs in Plate III. It 

 is to be observed that the smaller crviciform spicules, though usually displaced, 

 were in the living animals symmetrically arranged in the meshes. These smaller 



