302 



The zooecia are oval ; 7 in 2 mm. measured along the rows. Each long- 

 itudinal series is separated by a wavy line of close-set tubuli. 



In the longitudinal .section the median laminae are distinct, and in a por- 

 tion of the section the median tabuli ai-e shown. The primitive zooecia lie 

 along the median laminae, terminating at the entrance of the vestibule 

 where the posterior wall extends forward and constricts the aperture by 

 forming a superior hemiseptum. Beyond the septum the tube lies along 

 the posterior wall of the upper primitive zooecia for a distance of about 

 .2 mm. It then turns sufficiently to permit the zooecia to open perpendicu- 

 larly at the surface. The tube in the vestibidar zone is constricted notably 

 by the thickening of the walls. 



This species resembles R. fidelis and R. minima in having a well devel- 

 oped superior hemiseptum. It can be distinguished from R. fidelis by the 

 smaller zoarium. the decided construction of the zooecial tultes in the vesti- 

 bule and the direct apertures. 



The zoarium of R. minima is smaller and has less number of rows of 

 zooecia than R. Ichanonensis. 



Occurrence : Lebanon limestone, % mile south of Milesford, Rutherford 

 County, Tennessee. 



Holotype : 247-9. Indiana University. 



Genus Pachydictya Ulricli. Genotype : Pachydictya robusta Ulrich. 

 Pachydictya Ulrich, Jour., Cincinnati Soc. Nat. Hist, 5, 1882, p. 152. Foerste. 

 Bull. Sci. Lab. Denison Univ., 2, 1887, p. 152. Miller, N. A. Geol. Pal., 1889, p. 

 313. Ulrich, Geol. Surv. Illinois, 8, 1890, pp. 390, 522 ; Geol. Minnesota, 3. 

 1893, p. 145. Procta, Syst. Sil. Centre Boheme. 8. pt. 1, 1894, p. 15. Simp- 

 son, 14th Ann. Rept. State Geol. New York for 1894. 1897. p. 530. Nickles 

 and Bassler, Bull. U. S. Geol. Surv., 173, 1900. p. 48. Hennig, Arehiv. fur 

 Zool., K Sven. Vet.-ckad. Stockhalm, 2, No. 10. 1905, p. 25. Bassler. Bull. 

 U. S. Geol. Surv., 292, 1900, p. 57. Grabau and Shimer. N. A. Index Fossils, 

 1, 1907, p. 159. Cumings, 32d Ann. Rept. Dept. Geol. Nat. Res. Indiana, 

 1908, p. 751. Bassler, Bull. U. S. Nat. Mus., 77, 1911. pp. 137, 138. 



The zooecial apertures of Pachydictya are oval and have well developed, 

 ring-like walls; no hemisepta. The character distinguishes the genus from 

 any other of the family Khinidictyonidae. 



Pachydicfj/a scinli.s n. .s/j. Plate XIII, Figs. 1-3. Zoarium is ramose, 

 branches vary from 1 to 1.2 mm. in thickness and C to 10 mm. in width. The 

 margin is non-poriferous and variable in width, ranging from .2 to .0 mm. 

 Maculae of mesopores and raised clusters of zooecia occur Irreguhirly dis- 

 tributed over the surface. 



The zooecia are oval or circular, with well developed peristome, arranged 

 in indefinite longitudinal series ; and separated by irregular rows of minute 

 vertical tubuli in the peripheral zone. Deeper tangential sections show an 

 increased number and larger mesopores which in some places separate 

 the zooecia. 



The vertical section shows median tubuli traversing the median laminae 

 longitudinally. The zooecial tubes are recumbent only a very short dis- 



