110 THE CANADIAN NATURALIST. [Vol. ix. 



3. To the canal system, Professor Mobius does more justice, 

 and admits its great resemblance to the forms of this structure 

 in modern Foraminifera. This indeed appears from his own 

 figures, as will be seen from the fac-simile tracings reproduced 

 here, figs. 1, 2, 3 and 4, which well show how wonderfully this 

 structure has been preserved, and how nearly it resembles the 

 similar parts of modern Foraminifera. He thinks, however, 

 that these round and regularly branching forms are rather ex- 

 ceptional, which is a mistake ; though it is true that the sections 

 of the larger canals are often somewhat flattened, and that they 

 become flat where they branch. They are also sometimes altered 

 by a vicinity of veinlets or fractures, or by minute mineral seg- 

 refj-ations in the surroundinircalcite, accidents to which all similar 

 structures in fossils are liable. Another objection, not original 

 with him, is derived from their unequal dimensions. It is true 

 that they are very unequal in size, but there is some definiteness 

 about this. They are larger in the thicker and earlier formed 

 "layers, smaller or even wanting in the thinner and more super- 

 ficial. In some slices the thicker trunks only are preserved, the 

 slender branches having been filled with dolomite or calcite. It 

 is difficult, also, to obtain, in any slice or any surface, the whole 

 of a group of canals.* Farther, as I have shown, the thick 

 canals sometimes give off groups of very minute tubes from their 

 sides, so that the coarser and finer canals appear intermixed. 

 These appearances are by no means at variance with what we 

 know in other organic structures. Another objection is taken to 

 the direction of the canals, as not being transverse to the laminae 

 but oblique. This, however, may be dismissed, since Mobius 

 has of course to admit that it is not unusual in modern Foram- 

 inifera. It may be added that some of the appearances which 

 puzzled Mobius, and which are represented in his figures, evi- 

 dently arise from fractures displacing parts of groups of canals, 

 and from the apparently sudden truncation of these at points 

 where the serpentine filling gives place to calcite. It would also 

 have been well if he had studied the canal systems of those 

 Stroma toj)orce which have a secondary or supplemental skeleton, 

 as Ccenostroma and Caunopora. In illustration of this I give in 

 fig. 5 a group of these canals from a recent paper of my own.f 



* I have succt'edt-'d best in this by ctcliing the surface of broken 

 ispecimens. 



I Journal of Lcuidou G-eolugieal Society, January, 1878. 



