xlviii BRITISH GRAPTOLITES. 



1 . The successive buds developed in tubular cellules which are usually in contact 

 for a greater or less proportion of their length, and inclined towards the axis. 



(<i) Cellules in single series along one side of a common 

 solid axis. Stipes, two or more, from a common origin, 

 with or without a central disc. Sub-genera Monoprion, Dicly- 

 mograptus, Monograpkis, Tetragraptus, etc. 



(b) Cellules on one side of slender branches, which are 

 developed on one or two sides of a long slender axis or rachis, 



Graptolithus. the free extremities of which are likewise celluliferous. Ex. 



Gr. gracilis and Gr. divergent. 



(c) Cellules developed in parallel arrangement on two 

 sides of a common solid axis. Stipes narrow, elongate. Sub- 

 genus Diprion, = Diplograptus. 



(d) Cellules developed in a cruciform arrangement on the 

 Phyllogrwptus. four sides of a common or coalescent axis. Stipes elliptical 



or sub -elliptical. 



2. Cell-apertures, excavated in the margins of the stipes, without tubular or 



cup-form extension: the cell-apertures upon one or both 



Vluuacoijrajitus. ... 



sides of the stipe. Graptolithus bicornis and others. 



3. Solid axis eccentric or subexterior, with cellules developed in parallel 

 ranges on opposite sides of the stipe, and in contact throughout their entire 

 length. 



Betiolites. (a) Known only as separate stipes, with reticulate test. 



(b) Occurring as single stipes, and as compound fronds ; 

 test smooth. 



Beti.ograptus. 



II. 



Species having a common trunk, 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 bars) ; cellules in contact 

 Dendrograrptus. or closely arranged. 



2. Stipes mid branches more or less regularly united in a reticulate front, 

 Dictyonema. without elongate stem. 



:'». Branches unfrequently and irregularly connected by transverse processes. 



Callograptus. 

 1-. Stipes round or flattened, growing in groups, and bifurcating above; 



Inocaulis. margins denticulate; surface rough and scaly. 



