218 TWENTIETH REPORT ON THE STATE CABINET. 



b. Stipes simple at their origin, with cellules* 

 developed on the two sides near the base ; the 

 polypary becoming dichotomous above with a 

 single row of cellules on the outer margin of 



each division — or stipes growing in pairs from J- Dicranograptus, Hall. 

 an initial point, with the cell apertures in a 

 single series on the outer or lower side. Ex. 

 G. ramosus, G. sextans, G. divaricatus, and 

 others. 



3. Solid axis excentric or sub-exterior, with cellules 

 developed in parallel ranges on opposite sides of the 

 stipe, and in contact throughout their entire length. 



a. Known only as separate stipes, with reticulate | ^^^^^^^^^^^ Barrande. 

 test. j 



b. Occurring as simple stipes, and as compound 1 



„,.,,, } Retiograptus, Hall. 



fronds ; test smooth, J ' 



II. 



Species having a common trunk or stem, or growing in sessile groups of stipes 

 from a common origin, without distinct bilateral arrangement of the parts. Cellules 

 in single series on one side of the stipes or branches, and arranged along a common 

 canal or axis. 



1. Branches free (i. e. not connected by transverse j „ „ 

 , , „ , . i. i. 1 1 1 } Dendrograptus, Hall. 

 bars) ; cellules in contact or closely arranged. j 



2. Branches unfrequently and irregularly connected j ^ „ ,, 



, , > Callograptus, iifaZZ. 



by transverse processes. J ' 



3. Stipes and branches more or less regularly united 1 



in a reticulate frond, without elongate stem. | Dictyonema, Hall. 



4. Stipes round or flattened, growing in groups, andl 

 bifurcatins: above ; margins denticulate; surface 



rough or scaly. [The relations of this genus are not j ^ ' ; « • 



fully determined.} ) 



III. 



Slender cylindrical branches, with tubular cellules arranged in single (or in double?) 

 series. Cellules not in contact in any part of their length. Rastrites, Barrande. 



IV. 



Species having a common axis or rachis, with slender lateral alternating branch- 

 lets. Cellules unknown. Thamnograptus, ^aZ/. 



y. 



species having a common axis, more or less frequently bifurcating, with pinnulae 

 closely and alternately arranged on the opposite side; cell-apertures on one face of 

 the pinnulse closely and alternately arranged on the opposite sides ; cell-apertures on 

 one face of the pinnulae. Ptilograptus, Hall. 



VI. 



A simple flexuous rachis, with slender flexuous flattened pinnulse arranged in alter- 

 Bating order, at close and regular intervals, on the two sides. Cell-apertures unknown, 

 or circular. Buthograptus, Hall. 



VII. 



Strong stems, which are numerously branched. Branches and branchlets slender, 

 arranged in whorls. Cellules undetermined. Oldhamia [?], Forbes. 



