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tance, then turn outward and approach the surface almost direct. Two to 
six diaphragms cross the tubes in the vestibular zone. 
The mesopores are crowded with diaphragms in their earlier part, but 
closed at the surface by the thickened walls of the zooecial tubes. 
Pachydictya robusta is closely allied to this species, but the larger zoar- 
ium, and large zooecia of P. robusta serves to differentiate it. 
Occurrence: Pierce limestone, Murfreesboro, Tennessee. 
Holotype: 55140 U. S. Nat. Mus. 
Genus Trigonodictya Ulrich. Genotype: Pachydictya conciliatrix Ul- 
rich. Tigonodictya Ulrich, Geol. Minnesota, 3. 1893, p. 160. Nickles and 
Bassler,* Bull. U. S. Geol. Sury., 173, 1900, p. 49. 
“Zoarium of triangular branches, constructed upon the plan of Prismo- 
pora, but with zooecia and all minute details of structure as in Pachy- 
dictya.” 
Trigonodictya irregularis n. sp. Plate XIII, Figs. The zoarium con- 
sists of irregular, triangular branches with unequal poriferous faces. The 
edges are noncelluliferous. 
The zooecial apertures are oval, 7 to 8 in 2 mm. counted diagonally. The 
peristome, the structure of the interzooecial spaces, and the arrangement 
of the zooecia, show great similarity to Pachydictya foliata Ulrich. 
Straight and coalesced diaphragms occur in the zooecial tubes, varying in 
number from one to eight. 
The small tubuli, present in the interspaces of T'rigonodictya conciliatrix 
and the longitudinal arrangement of the zooecia, serve to distinguish it from 
this species. 
Occurrence: Lebanon limestone; 2 miles southwest of Christiana, Ruth- 
erford County, Tennessee. 
Holotype: 245-11. Indiana University. 
New Genus Hemidictya. Zoarium bifoliate fronds or irregularly ramose 
forms with nonporiferous margins; surface with maculae; zooecia with 
thin walls, elliptical or subcircular; vestibule nearly direct, walls thicken 
and form peristomes:; diaphragms appear in some of the vestibular tubes; 
inferior and superior hemiseptum present; spaces between the vestibule 
traversed by one or more series of minute tubuli. The presence of a peri- 
stome shows the close relation of this genus to Pachydictya, from which it 
is distinguished by the occurrence of hemisepta. 
Genotype: Hemidictya lebanonensis, n. sp. 
Hemidictya lebanonensis n. sp. Plate XIV, Figs. 1-5. Zoarium consists 
of thin fronds, 5 to 10 mm. across and one mm. thick, from the edge of 
which rise several compressed short branches 2.5 to 3 mm. wide and .3 to .5 
mm. thick. The margin is conspicuously non-poriferous in the angle of 
bifurcation, where it is .5 mm. wide in the type specimen, and becomes 
narrower rapidly farther along the branch. 
The surface is even, upon which is distributed small subsolid macules, 
*Nickles and Bassler, Bull. U. S. Geol. Surv., 173, 1900, p. 49. 
