152 TABULATE CORALS. 



XXIII., 1876) that there are no tabula; in Pleurodiciytim, these 

 structures being quite as well developed as could be expected 

 in such short tubes. 



Formation and Locality. — Hamilton group (Devonian), 

 Hamburg, State of New York, Coll. George J. Hinde. (Judg- 

 ino- from the figures, it would seem not improbable that the 

 coral described by Prof. Ferd. Roemer in the ' Silurian Fauna 

 of West Tennessee,' p. 19, i860, under the name of Calamopora 

 Forbesi, var. discoidca, may be really a species of Pleurodictyuni 

 allied to P. stylophorum, Eaton. It is probable, also, that the 

 nummiform species of Michclinia alluded to by Dr Rominger 

 in the ' Foss. Corals of Michigan,' p. 72, as occurring in the 

 Upper Silurian strata of North America, are referable to 

 Pleurodictyum, if the latter genus is to be kept distinct.) 



Gemts Chonostegites, Edwards and Haime, 185 1. 



(Pol. Foss. des Terr. Pal., p. 299.) 



HaiiiicophyUum, Billings, Canad. Journ., new sen, vol. iv. p. 139, 1859. 



Gen. Char. — Corallum forming large subhemispherlcal, sub- 

 fasciculate masses, composed of cylindrical corallites, which grow 

 side by side, and are annulated by numerous close-set, hollow, 

 periodic expansions, which alternate with as many circular con- 

 strictions. For the most part the corallites are separate, except 

 that they are united by the periodic expansions above spoken 

 of, which thus form a succession of concentric floors, connecting 

 the tubes with one another. In the parts between these periodic 

 floors the corallites are enclosed each by a distinct epitheca, and 

 the walls are imperforate. There are, however, often parts of 

 the corallum in which the walls of contiguous corallites are in 

 close contact, and then numerous " mural pores " are developed. 

 Tabulae numerous, arched, often uniting with one another in 

 such a way as to give rise to a loose and open subvesicular 

 tissue, which is continued into the hollow periodic expansions 

 of the corallites. Septa in the form of short spines in the in- 



