CARBONIFEIiOUS PERIOD. 107 



of minute, dimorphous pores upon the axial portion of the poriferous side 

 of the stem and branches, and also in the absence of the three longitudinal 

 i-aised lines that distinguish that species. 



Position and locality. — Strata of the Carboniferous period; at the con- 

 fluence of White Mountain and Black Rivers, Arizona. 



Genxts SYNOCLADIA King, 1849. 



Synocladia biserialis Swallow. 



Plate VII, fig. .3 a, h, and c. 



Synocladia biserialis Swallow and Hawn, 1858, Trans. Acad. Sci. St. Lonis. i, 179. 

 Synocladia viryulacea Geinitz, 186G, Oarbonformat. nnd Dyas in Nebraska, 70. 

 Synocladia biserialis Meek, 1872, U. S. Geol. Surv. Nebraska, 156. 



Polyzoary probably infundibuliform, but the specimens usually found 

 consist only of spreading frond-like fragments ; primary branches a little 

 larger than the others, the latter increasing by divergence at various angles 

 from the primary branches, also occasionally from each other, and rarely 

 by starting upward from the middle of a dissepiment ; dissepiments cellu- 

 liferous, a little nan'ower than the branches, and arching upward a little as 

 they extend from branch to branch ; fenestrules irregularly four-sided ; 

 upper side usually convex, and lower side sometimes concave, about nine 

 in the length of a centimeter, measuring upward, generally wider than the 

 branches, but occasionally narrower, especially near the base of the poly- 

 zoary. Upon the poriferous side, the branches and dissepiments, especially 

 the former, are each provided with an irregular mesial carina, consisting of 

 small, elongate, confluent nodes, which are sometimes sharp and prominent. 

 Cell-apertures moderately large, rounded, borders prominent ; cells arranged 

 in single, quite distinct lines, one on each side of the mesial carina of the 

 branches, and generally each dissepiment bears a double row of similar 

 cells. Upon some of the dissepiments the cells form only a single row at 

 the middle, while upon others they are not only double but another cell is 

 added near the junction with the branch, giving three cells abreast at those 

 points. 



Professor Geinitz and others have referred this species to S. virfjulacea 

 as only varietally different from the typical forms of that species. S. 



