Maryland Geological Survey 235 



Tangential sections show large astrorhizEe which usually have an axial 

 tube and stout branches. Skeletal tissue dense, ends of vertical pillars not 

 distinct. The skeletal tissue is much denser than in other species of the 

 fauna, presenting a fine granular appearance in sections. 



This form differs from other species of the fauna in having a finer re- 

 ticulated fiber, much more distant horizontal laminse, and much larger 

 tubular spaces between the vertical pillars, imparting a much coarser 

 appearance to the structure than that observed in other forms. Sections 

 of some specimens cut a little obliquely appear as if without regular ar- 

 rangement as shown on the accompanying plate. Such specimens seem to 

 agree so closely with Parks' Stromatopora clarkei as to lead the writer to 

 believe that the latter species may be identical with this. ;S'. clarkei also 

 occurs in the same general faunal association as this species does in Mary- 

 land. Abundant in the Eawlings Stromatopora reef about 50 to 60 feet 

 above the base of the Keyser member, associated with Cladopora recti- 

 lineata. It occurs also at Cedarville, New York. 



Occurrence. — Helderberg Formation, Keyser Member. Cut of Bal- 

 timore and Ohio Eailroad south of Cookerly. 



Collection. — Maryland Geological Survey. 



Syringostroma centrotum Girty 

 Plate XXVIII, Figs. 5, 6 ; Plate XXX, Fig. 2 



Syringostroma centrotum Girty, 1894, 48th Kept. N. Y. State Mus., vol. ii, p. 



293, pL vii, figs. 1, 2. 

 Syringostroma centrotum Parks, 1909, Univ. Toronto Studies, Gaol. Ser., 



No. G, pp. 12-14. 

 Stromatopora centrota Grabau and Shimer, 1909, N. Amer. Index Foss., vol. i, 



p. 45, fig. 72. 



Description. — " No specimens in this collection are entire, but all evi- 

 dence points to an originally spheroidal form for the ccenosteum. One 

 specimen appears to have had a diameter of about 27 cm. when entire. 

 The concentric character of the structure is usually quite striking. Some 



specimens are readily separated into thin sheets or latilamina? 



Tangential sections do not remain parallel to the surface in this species, 

 except over small areas, for the curvature is not regular but flexuous, and 

 the latilaminEB are more or less foliaceous and imbricating. Thus ex- 



15 



