taiicp. then turn outwanl mikI iij.i.ro.Mcli the sni'fMi'c aliiK.st direct. Two lo 

 six diaphrugms cross tlie tultcs in the vcsliluihir zdiic. 



The nies()i)ores are crowded with diiiplirii.mns in tlicir (•;irlicr icirt. I)nt 

 closed at the surface hy the thickened walls of the /o<ic(i;ii tulics. 



Pachydictya rohnsta is closely allied to tliis si.ccics. but tlie larger zoar- 

 ium. and larjje zooecia of P. rohiixta serves to differentiate it. 

 Occurrence: Pierce limestone. Mnrfreesboro, Tennessee. 

 Holotype: ;jr)140 U. S. Nat. Mus. 



Oenus Trigonodictya IJlrich. Genotype: Tachydictya conciliatrlx T'l- 

 rich. Tisonodictya TJIrich. Geol. Minnesota. .'!. 1S!>:;, p. icO. Xicklcs and 

 Hassler.* Bull. U. S. (Jeol. Surv., 17:'.. ITMIO. p. 4!>. 



"Zoarinni of triaiifinlar branclies. constructed ui>oii liie plan of Prisnio- 

 I)ora. Init with zooecia and all minute details of structure as in Pachy- 

 dictya."' 



Trigouodictj/n irregularis ii. sp. Plate XIII, Figs. The zoarium con- 

 sists of irregular, triangidar branches with unequal poriferous faces. The 

 edges are noucelluliferous. 



The zooecial apertures are oval. 7 to S in 2 nmi. counted diagonally. The 

 peristome, the structure of the interzooecial spaces, and the arrangement 

 of the zooecia. show great similarity to Pachydictya folinta Ulrich. 



Straight and coalesced diaphragms occur in the zo(»ecial tubes. vai\ving in 

 number from one to eight. 



The small tubnli. present in the intersiiaces of Trif/ojiodicfyd concUintri.r 

 and the longitudinal ariangement 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 I^niversity. 



New Genus Hcmidictya. 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 i>eristomes ; 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 tubnli. The in-esence of a peri- 

 stome shows the close relation of this genus to Pacliydict.xa. from which it 

 is distinguished by the occurrence of hemisepta. 

 Genotype: Hemidictya lebanonensis. n. sp. 



Hemidictyti hlKnumciisis it. .s/>. Plate XIV. Figs. i:!. Zoarium consists 

 of thin fronds. ."» to 10 mm. across and one nim. thick, from the edge of 

 which rise several compressed short branches 2.."> to ."! mm. wide and ,.3 to ..") 

 mm. thick. The margin is conspicuously iioii-poiifeidus in the angle of 

 bifurcation, where it is ."> mm. wide in the tyjie specimen. ;iiid becomes 

 narrower rapidly farther along the branch. 



The surface is even, upon which is distribnteil small snbsolid macules. 



'Nifkles and Bassler, Bull. U. S. Gool. Surv., 17:1, 1900, p. 49. 



