182 



TWENTIETH REPORT ON THE STATE CABINET. 



Fig. 22. 



GrAPTOLTTHUS (DiPLOGRAPTUS) PEI8TI8. 



The species of this type [Diprion or Diplograptus) are simple linear or 

 sub-linear stipes, bearing" a range of cellules on each side, often showing 

 an initial point or radicle at the base, and an extension of the slender axis 

 above and beyond the eelluliferous portion. This axis is sometimes divided, 

 showing it to be composed of two distinct laminae, but this condition is 

 extremely rare among American specimens. 



From these forms with a double series of cellules, we pass to the broad 

 filiform stipes, which are apparently composed of four semi-elliptical parts 

 conjoined along their straight sides, and thus present four ranges of cellules. 

 These forms {Phyllograptus) are, in some species, broad and short, while 

 others are elongate, with sub-parallel sides, as shown in the accompanying 

 figures, and it may not always be possible to distinguish them from 

 Diplograptus. 



