298 



The zoecia are subpentagonal. thin-wallod aiul completely separated by 

 mesopores ; 4 to 5 occux' in 2 mm. 



The mesopores are only slightly smaller than the zooecia, of more irreg- 

 ular shape, thinner walletl and usually six-sided as seen in the tangential 

 section. In the younger stages they are zooecial-like, with few or no dia- 

 phragms, becoming smaller in the mature region and crossed by 2 to 3 dia- 

 phragms in the distance of their own diameter. The smaller mesopores are 

 distinctly beaded. The zooecia increase in size with age. and have few 

 and irregularly spaced diaphragms ; one to two in the primitive portion, 

 and rare or absent in the peripheral zone. The acanthopores are large, 

 thin-walled and have a well developed central lucid area. They occur at 

 the angles of the zoecia and mesoiM)res and are a little more numerous than 

 the zoecia. 



The characters of the tangential section separate this siiecies from any 

 described Stroma totrypa. 



Occurrence: Pierce limestone, at the ford IVo niile southeast of Black- 

 man, Rutherford County, Tennessee. 



Holotoype : 245-16. Indiana University. 



ORDER CRYrTOSTOMATA vine. 



The delinition of the order, as given by I'lrich in the English edition of 

 Zittel's Textbook of Paleontology, and again repeated by Bassler in the 

 Zittel-Eastman edition, i)ultlisluMl in 19i:'>. is as follows: 



"Primitive zooecium short, pyriform to oblong, quadrate or hexagonal, 

 souietiiiies tubular, the aperture anterior. In the mature colony the aper- 

 tui-e is cdiiceaU'd. occurring at the bottom of a tubular shaft ("vestibule"), 

 which may be intersected by straight diaphragms or hemisepta, owing to 

 the direct super-imposition of layers of polypides : vestibular shaft sur- 

 rounded by vesicular tissue, or by a solid calcareous deposit; the external 

 orifice roundi'd. M;irsupia and avicularia wanting." 



Family rtUodictyonidac Llrich. 



Zoarium bifoliate, composed of two layers of zooecia, grown together 

 back to back, forming leaf-like expansions, or compressed branching or in- 

 osculating stems, that are usually jointed, at least at the base; mesotheca 

 without median tubuli : zooecia usually have hemisepta and semielliptical 

 oritices ; apertures usually ovate, surrounded by a sloping area or a distinct 

 peristome; vestibules M'parateil by thick walls. 



acnns Oraptodivljia 11 rich, (ienotype : I'tilodictya perelegans Ulrich. 

 (iraptodictya TUrich. Jour. Cincinnati Soc. Nat. Hist., 5, 1882, pp. 151, 165. 

 Miller, N. A. Geol. Pal., 1S89, p. 307. ITlrich. Geol. Surv. Illinois, 8, 1890, 

 p. 39.3. Procta, Syst. Sil. Centre Beheme. s, pt. 1, 1894, p. 14. Simpson, 14th 

 Ann. Rept. New York State Geol. for 1SII4, 1897, p. 541, Nickles and Bass- 

 ler, Bull. U. S. Geol. Surv., 173, 1900, p. 46. Cumings, 32d Ann. Rept. Dept. 

 Geol. Nat. Res. Indiana, 1908, p. 747. Bassler, Bull. U. S. Nat. Mus., 77, 

 1911, p. 121, 



