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 séction the median tabuli are 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 
2mm. It then turns sufficiently to permit the zooecia to open perpendicu- 
larly at the surface. The tube in the vestibular 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 tubes 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. lebanonensis. 
Occurrence: Lebanon limestone, 14 mile south of Milesford, Rutherford 
County, Tennessee. 
Holotype: 247-9. Indiana University. 
Genus Pachydictya Ulrich. Genotype: Pachydictya robusta Ulrich. 
Pachydictya Ulrich, Jour., Cincinnati Soc. Nat. Hist., 5, 1882, p. 152. Foerste, 
3ull. 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, Archiv. fur 
Zool., K Sven. Vet.-ckad. Stockhalm, 2, No. 10, 1905, p. 25. Bassler, Bull. 
U. S. Geol. Sury., 292, 1906, p. 57. Grabau ané Shimer, N. A. Index Fossils, 
1, 1907, p. 159. Cumings, 32d Ann. Rept. Dept. Geol. Nat. Res. Indiana, 
1908, p. 751. Bassler, Bull. U. 8S. 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 Rhinidictyonidae. 
Pachydictya senilis ». sp. Plate XIII, Figs. 1-3. Zoarium is ramose, 
branches yary from 1 to 1.2 mm. in thickness and 6 to 10 mm. in width. The 
margin is non-poriferous and variable in width, ranging from .2 to .6 mm. 
Maculae of mesoperes and raised clusters of zooecia occur irregularly 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- 
