142 THE CANADIAN NATURALIST. [Vol. vii. 



'flexuous, and confined to the central portion of the coral." 

 (Billings.) 



The internal structure which distino-uishes corals of the genus 

 ''Heliojjhyllum is thus of a somewhat complicated nature. The 

 septa are well developed and extend nearly or quite to the centre 

 of the theca, where they are often somewhat twisted ; but there 

 IS no columella. A central tabulate area exists, but is of compa- 

 ratively circumscribed dimensions. Externally to this tabulate 

 urea, the interseptal loculi are divided into cells or small com- 

 partments by the intersection of two sets of dissepiments having 

 diiferent directions. The dissepiments of the first and most con- 

 spicuous set are directed from the internal surface of the wall 

 obliquely inwards and upwards towards the centre, in a succes- 

 sion of arches, the convexities of which are turned upwards. 

 These dissepiments doubtless correspond with that circumferen- 

 tial portion of the tabulae, which is bent downwards towards the 

 base of the coral in species of Zajjhrentis, ClUiophyllmn, Dipliy- 

 pliyllmn^ &c. When these dissepiments are more or less imper- 

 fect or have suffered destruction, they leave upon the flat sur- 

 faces of the septa a corresponding number of arched strife or 

 ridges. Similarly, in the calice of the coral these dissepiments 

 appear on the free edges of the septa as so many short spines. 

 The dissepiments of the second series are more delicate, more 

 discontinuous, and much more variable in direction than those 

 of the preceding series. Sometimes they are nearly vertical, or, 

 in other words, are pretty nearly concentric with the theca. 

 Sometimes they are not far from the horizontal, and intersect the 

 dissepiments of the former series at a very acute angle. Most 

 commonly they are directed inwards and downwards from the 

 theca towards the centre, so as to cut the dissepiments of the 

 preceding series nearly at right angles. Decorticated examples 

 <d^ Heliopliyllum exhibit a most characteristic appearance, due to 

 the intersection of the septa and fiUed-up interseptal loculi with 

 the dissepiments of the first mentioned series. In this way is 

 produced a succession of vertical ridges and intervening sulci 

 crossed by numerous curved or sharply zig-zagged encircling ridges. 

 The species of Heliophyllum which have been described by 

 Mr. Billings as occurring in the Devonian rocks of Canada, are 

 'H. JEi'iense, H. Cayugaense, H. Canadense, H. exigiium, H. 

 coUigatum, H. SaUi, and H. temdseptatiim. the first five from 

 the Corniferous formation, and the last two from the Hamilton 



