W. D. Lang —Calciwm Carbonate and Evolution. 73 
measure and describe the materials brought up, and to put the 
results on record. This work has been facilitated in every way by 
the boring firms engaged. 
For several suggestions and general encouragement the writer is 
indebted to Mr. T. C. Cantrill, of the Geological Survey. 
ViI.—Caucruom Carponare AND Evoturion 1n Ponyzoa.! 
By W. D. Lane, M.A., F.G.S. 
te a review in the Grotogicat Magazine for 1913? of an important 
paper by Cumings on the development and systematic position of 
the Monticuliporoids, it was pointed out that the elucidation of the 
post-embryonic stages of that group conclusively proved them to be 
Polyzoa, and disposed of Kirkpatrick’s contention that they were 
allied to Merlia, a recent siliceous sponge. Thus, further to prove 
the dissimilarity between the Monticuliporoids and IMerlia is to flog 
a dead horse. Nevertheless we welcome the excellent figures by 
Cumings and Galloway of the microscopic structure of the two 
organisms showing that the skeleton of the one is formed of super- 
posed layers and the other of radiate spicules so adjusted as to form 
a mesh-work. 
The authors, however, are not mainly concerned with the connection 
of Merlia and the Monticuliporoids, but with the Trepostome wall 
and various correlated structures, namely Cysts and Cystiphragms, 
Intrazocecial spines, Acanthopores and Communication-pores. They 
point out that Communication-pores of Paleozoic Trepostomata 
resemble those of Heteropora—a form that persists until recent times ;_ 
‘that Acanthopores are the continuations below the general zoarial 
surface of hollow spines, ‘‘ undoubtedly protective’? in function, 
which, in unworn specimens, project above the surface ; that ‘‘ certain 
extraordinary spines projecting into the submature region of zocecia 
“of a species of Nicholsonella’’ resemble those of Heteropora neozelaniea, 
as figured by Nicholson. They make the very interesting and 
ingenious suggestion that Cysts and Cystiphragms are the expression 
of the renewal of the polypide on the formation of a Brown Body 
(a familiar process among recent Polyzoa) and that the purpose of 
the ectocyst in laying down a fresh wall at each such crisis is the 
‘restriction of intrazocecial space’’; moreover, the occurrence of 
minute concretions of some iron compound in the Cyst, i.e. the space 
enclosed by the cystiphragms, is claimed to be produced by the decay 
of the degenerated polypide. 
Finally, the structure of the wall is considered. Hitherto it has 
been customary to divide the Trepostomata by their walls into two 
groups—lIntegrata, those that have a dark median line in the wall in 
virtue of which each half is claimed for that zocecium adjoining it— 
and Amalgamata, in which there is no dark line, but the walls of two 
1 [Originally written as a review on ‘‘ Studies of the Morphology and 
Histology of the Trepostomata or Monticuliporoids’’, by E. R. Cumings and 
J. J. Galloway, 1915, Bull. Geol. Soc. America, Vol. xxvi, pp. 349-374, 
Pls. 10-15, but considered more appropriate as an original paper.—ED. | 
2 GEOL. MAG., Dec. V, Vol. X, pp. 32-36. 
