214 



REPORT ON THE STATE CABINET. 



Fig. 25. 



not unlike some of the Graptolites (Monograptus) proper, witli the parts 

 in bilateral arrangement. 



In the Genus Rastrites of Barrande, we find a departure from all of 

 the preceding forms, in the slender stipes with delicate slender tubular 

 cellules. The species of this genus, so far as known, 

 have the cellules developed on one side only of the stipes 

 or branches; though there seems no reason why we 

 should not have species with cellules upon the two sides 

 of the axis (fig. 25, Rastrites harrandi). 



The species for which I have proposed the name 

 Thamnograptus, consist of slender cylindrical stipes and 

 branches, some of them very similar in general aspect 

 to Rastrites ; but the alternating branches are long and 

 slender, and we ' fig. 2s. 



have found no ap- 

 pearance of cellules on any part of 

 the specimens known. 



In Thamnocfraptus typus (fig. 26), 

 the branchlets are given ofi" altern- 

 ately on the opposite sides of a stipe 

 or rachis, and the slender solid axis 

 can be traced from the main stipe 

 Fig. 27. into and along the 



centre of the branch- 

 lets. The analogy 

 between these forms 



and the celluliferous Graptolites of the preceding illusti'a- 

 tions does not appear to be very intimate, but they occur 

 in the same beds, and the fossil has the same texture and 

 substance. 



In the Genus Ptilograptus (Plate iv), we have a some- 

 what analogous mode of growth, but there is always an 

 aspect or expression of the fossil which distinguishes it 

 from Thamnograptus. In one species of Ptilograptus, 

 moreover, cell-apertures have been detected on one side 

 of the branches or pinnulte. 



In the Buthograptus (fig. 27, B. laxus, enlarged), we 

 have a form bearing some analogies with the preceding ; 

 but the rachis is flexible, and is not known to be branched. 



