Development oj Tetradium Cellulosum Hall. — Rnedeiiimin. 17 
development of the corallites by successive sections and thus 
removes some of the doubts which, judging from the litera- 
ture on that genus, still exist. 
A short review of the literature will best show what rela- 
tions of the genus are so insufficiently known that they have 
been made the special subject of research by the writer. 
Dana*, having used a fossil from an unknown locality, 
characterized the genus as follows: "Corallum massive, con- 
sisting of 4-sided tubes, and cells with thin septa or parietes; 
cells stellate with four narrow laminae," which characteriza- 
tion enabled Prof. Safford to discover the coral in the Ordo- 
vician of middle Tennessee. Prof. Safford, for the first time, 
gave a full description of the genus, which he placed among 
the tabulates, and described several forms. f The most im- 
portant of his observations for our investigation are the fol- 
lowing: The tubes are most frequently united throughout 
laterally, forming massive coralla. The increase appears to be 
by division of the tubes, the latter splitting sometimes into 
two cell-tubes, not infrequentl\- perhaps into four; opposite 
lamina; united form the new walls of the young cells, each 
of which is in the meantime supplied with its four ra^'s. 
These rays, however, were regarded by Prof. Safford as not 
solely serving the process of fission, but also as being of the 
character of septa, as the following quotations show: "This 
group we regard as being allied in some respects to the Fa- 
vositidcE, while on the other hand, the cruciform arrangement 
of the lamella? unite with the Zoaiitharia rugosa of MM. Milne 
Edwards and Haime; in fact it appears to afford an inter- 
esting type of the quadripartite character of the lamellae, first 
pointed out b\' these distinguished authors in many pahvo 
zoic corals." And in the description of Tetradiuni fibratu))i 
Saff., it is said "The four lamelhf, distinct, nearly reaching 
the centre of the tubes." 
Prof. G. Rominger,J ten years later, shows by a remark 
of his that he had recognized the fission of the corallites of 
*U. S. Exploring Expedition during 1838 to 1842 under command of 
Charles Wilkes, vol. VIII, p. 701. 
tj. M. Safford; Remarks on the genus Tetradiuni, with notices of 
the species found in middle Tennessee, Am. Jour. Sci., \o]. 22, 1856, p. 
236. 
^Observations on Chcetctes and some related genera, Proc. Acad. 
Nat. Sci. Philadelphia, 1866, p. 113. 
