1864,] , DAWSON STRUCTURE OF EOZOON. 53 



in their massive style of growth to the forms now xxndcr consider- 

 ation. 



These reasons are, I think, sufficient to justify me in regarding 

 these remarkable structures as truly organic, and in searching for 

 their nearest allies among the Foraminifera. 



Supposing then that the spaces between the calcareous laminee, as 

 well as the canals and ttibuli traversing their substance, were once 

 filled with the sarcode body of a Rhizopod, comparisons with modern 

 forms at once suggest themselves. 



Prom the polished specimens in the Museum of the Canadian Geolo- 

 gical Survey, it appears certain that these bodies were sessile by a 

 broad base, and grew by the addition of successive layers of chambers 

 separated by calcareous laminae, but communicating with each other 

 by canals or septal orifices sparsely and irregularly distributed. 

 Small specimens have thus much the aspect of the modern genera ' 

 Carpenter id and Polytrema. Like the first of these genera, there 

 would also seem to have been a tendency to leave in the midst of 

 the structure a large central canal, or deep funnel-shaped or cylin- 

 drical opening, for communication with the sea-water. AVhere the 

 laminaj coalesce, and the structure becomes more vesicular, it 

 assumes the " acervuline " character seen in such modern forms as 

 Nuhecidaria. 



Still the magnitude of these fossils is enormous when compared 

 with the species of the genera above named ; and from the specimens 

 in the larger slabs from Grenville, in the Museum of the Canadian 

 Survey, it would seem that these organisms grew in groups which 

 ultimately coalesced and formed large masses penetrated by deep irre- 

 gular canals, and that they continued to grow at the surface while the 

 lower parts became dead and were filled up with infiltrated matter or 

 sediment. In short, we have to imagine an organism having the habit 

 of growth of Carpenteria, but. attaining to an enormous size, and by 

 the aggregation of individuals assuming the aspect of a coral-reef. 



Mr. Billings has described two remarkable species from the Cal- 

 ciferous formation at Mingan, referred by him to the new genus 

 Archceocyathus, which he places, with doubt, among Protozoa. If, 

 as I believe, correctly referred to this group, their calcareous-cham- 

 bered skeletons would place them with Foraminifera rather than 

 with Sponges. The mode of growth of Arclueocyathws is cylindrical 

 or inverted conical, with a hollow axis. In one of the species, A. 

 Minganensis, this hollow cylinder is very Avide, and the chambers 

 are arranged in a radiating manner. In the other, A. atlanticus, 

 the central canal is narrower, and the chambers have thick walls 

 and are more irregularly disposed. These fossils, in the general 

 arrangement of their parts, appear like gigantic representatives of 

 Nuhecularia and Dactylopora, though different in details. They are 

 evidently generically distinct from the Laurentian fossils ; but if, as 

 I think probable, calcareous Rhizopods, they resemble the specimens 

 now under consideration in the dev^elopment of such structures into 

 coral-like forms and dimensions, and this at an early, if less remote, 

 geological period. 



