390 GEOLOGY AND MINERALOGY. 



G. caducevs, (Didi/mograpsus caduceus, Salter). Branched; the branches 

 deeply recurved, and toothed on the outside. Long filiform rachis. Fig. 3. 

 Sillery formation ; opposite ' : bee. 



To this section belong also the European forms— G. SedgmeHi, Portlock; 

 G. fJjiplograpsus) folium, etc. 

 S 2. GraptolUes vith acute or wb-rnueronate ncrraturc-s. 



G. pristis, Hall. (Diplograpsus pristis, Prionotis pristls. Hisinger). Un- 

 branched. Sripe with central filiform rachis, and teeth on each side; the tips 

 sometimes sub-mucronate. Fig. 4. Trenton limestone, Utica slate, and Hudson 

 River group . G. amplexieaule and G. secalinus, Hall, are probably varieties. 



G. priodon, Bronn. G. Ladenm* t Murchison : Silurian system. G. Clinton- 

 ensit, Hall). Unbranched ; toothed on one side only. Teeth deeply cut, and 

 with recurved tips. Fig. 5. Clinton group. In Europe, in Lower and Upper Si- 

 lurians. 



G. Sagittarius, Portlcck. Unbranched. Stipe in long narrow pieces, straight 

 or slightly flexuous, with acute teeth on one side only. Fig. 6. Hudson River 

 group. 



(r . tenuis, Portlock. Unbranched. Stipe in long thread-like pieces, straight or 

 flexuous, obscurely and distantly toothed on one side only. Fig. 7. Hudson River 

 group. 



G. srrrahdus, Hall. Branched : the branches widley divergent, very slender, 

 and with somewhat distant teeth. Fig. 8. Hudson River group, Albany. 



G. gracilis, Hall. In delicate, wavy branches. See Pal. New York ; vol. 1, 

 p. 274. 



G. venosus, Hall. See Pal. New York; vol. 2, p. 40. 

 .:' -':. GraptolUes with obtuse serratures. 



G. bicornia, Hall. Unbranched. Stipe tapering towards the base, and termi- 

 nating in a short fork. Toothed on each side : teeth obtuse. Central rachis usu- 

 ally well pronounced. Fig. 9. Hudson River group. 



G. furcatus, Hall. Branched: the branches near together and converging; 

 bluntly toothed, in general, on both sides. Fig. 10. Hudson River group, Albany. 

 G. ramosus, Hall. Branched: the branches diverging at a moderate angle, 

 long, and toothed on the outside only. Fig. 11 . Hudson River group. 

 g 4. GraptolUes with smooth borders.* 



G. scalaris* Unbranched. Stipe alternately spotted, or transversely marked 

 on each side, but with smooth margin. Gradually tapering, and terminating in a 

 slight expansion. Fig. 12. Hall. Utica slate and Hudson River group. 



This form differs very materially from the G scalaris, described by Geinitz, in 

 Bronn's Jarbuch for 1840 and 1842. It has rather the aspect of a G. bicornis 

 flattened in a plane more or les3 perpendicular to the direction of the teeth. 



G. hevis, Hall. Unbranched. Stipe narrow, flexuous, and slightly tapering. 

 Utica slate (A doubtful form). 



For more complete descriptions, <Scc, of the above species, the reader is referred 

 to the standard work on the Palajontology of New York, by Professor James Hall. 

 Our knowledge of the graptolites generally, is likely to receive considerable addi- 

 tions from some of the projected publications of the Geological Survey. 



E. J. C. 



* Probably a deceptive appearance, produced by flattening in a particular direction. 



