201 



nor are any signs of septa to be observed until just before a tube divides 

 when the characteristic four septa of Tetradium are developed. A normal 

 corallite is quadrangular and about two-thirds of a millimeter across. 



Occurrence. STONES RIVER LIMESTONE. Abundant especially in the 

 upper division, in the Appalachian Valley. In Maryland exposures along 

 the line of outcrop from Pinesburg Station north through Wilson to the 

 state line exhibit numerous examples. 



Collections. Maryland Geological Survey, U. S. National Museum. 



TETRADIUM COLUMNARE (Hall) 

 Plate XLI, Fig. 4 



Chaetetes columnaris Hall, 1847, Pal. New York, vol. i, p. 68, pi. xxiii, 



figs. 4, 4a. 

 Tetradium columnare Safford, 1856, Amer. Jour. Sci. and Arts, 2d ser., 



vol. xxii, p. 237. 



Description. " Coral massive, hemispherical or subglobose, consisting 

 of a series of parallel or diverging polygonal tubes; tubes four- or five- 

 sided, simple, without visible transverse dissepiments or connecting pores ; 

 interior of the cells apparently rugose or denticulate. 



" The rugose structure within the cell probably indicates the existence 

 of diaphragms which have disappeared. The fossil, in its general form 

 and structure, has the appearance of a Favosites, from which a cursory 

 examination would not induce us to separate it. A closer examination 

 proves that the tubes are usually four-sided, and that there are no con- 

 necting pores in the walls of the cells. These characters had decided me 

 to separate it from the genus Favosites, before knowing fully the char- 

 acters on which the genus Chaetetes is founded. It appears referable 

 to the latter genus from its general similarity to some of the species, the 

 character of quadrangular cells probably being unimportant and not 

 constant. The apparent absence of diaphragms, or transverse dissepi- 

 ments, is perhaps due to their subsequent destruction, or solution and 

 removal." Hall, 1847. 



Occurrence. CHAMBERSBDRG LIMESTONE ( Caryocystites bed). Fort 

 London, Pennsylvania. 



