200 SYSTEMATIC PALEONTOLOGY 



abundantly in the lower Beekmantown just above the top of the Stone- 

 henge member, where it appears in lamellose masses on the weathered 

 rock surfaces. Unfortunately all trace of the structure is lost in the 

 solid rock and the generic determination cannot therefore be confirmed 

 by thin sections. The corallites are polygonal, with rather thick walls 

 which sometimes show a distinct line of separation. Three corallites 

 occur on an average in 2 mm. No septa are seen, but their apparent 

 absence may be due to the poor preservation of the specimens. ' The 

 vertical sections exposed by weathering show no tabulae. 



If this species should prove to be an early representative of Tetradium 

 it will be readily distinguished from the other species of that genus by its 

 small corallites. 



Occurrence. BEEKMANTOWN LIMESTONE. Just above the Stonehenge 

 member. The best specimens were found in the old brick yard on the 

 eastern edge of Hagerstown. 



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



TETRADIUM SYRINGOPOKOIDES Ulrich 

 Plate XXXVIII, Figs. 13-15 



Tetradium sp. Bassler, 1909, Va. Geol. Surv., Bull., vol. iia, pi. iv, fig. 2. 

 Tetradium syringoporoides Ulrich, 1910, in Stose, Folio U. S. Geol. Surv., 

 170, p. 58. 



Description-. This species, which is very characteristic of the Stones 

 River group, has been known for a number of years by the students of 

 Appalachian geology as the " single-tubed Tetradium." Certain beds of 

 the Stones River limestone are so charged with these tubes that they give 

 the rock a coarse, spongy appearance. Upon weathering the individual 

 tubes stand out in relief like pieces of cord, but in fractured fragments 

 of limestone the tubes are equally distinct, although here appearing as 

 stringers of calcite. Upon close examination the coral nature of this 

 organism becomes evident, for the tubes divide, giving rise to either two 

 or four individual tubes which, after adhering together for a short dis- 

 tance, separate and in turn subdivide as before. No tabulae are visible 



