124 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



In order to make this notice as complete as possible with the materials 

 I now possess, I have, with few exceptions, given illustrations of the species 

 known to me as occurring in this sandstone in the Upper Mississippi valley. 



GRAPTOLITID^. 



GENUS DENDROGRAPTUS ( Hall). 

 DENDROGRAPTUS HALLIANUS (Prout). 



Graptolithus hallianus : Prout, Am. Jour. Science (2), xi, p. 187, 1851. 



Frond proceeding from a distinct root. Stems strong, numerously 

 branched : branches divaricating, and frequently subdivided j 

 divisions serrate or celluliferous ; cellules numerous, little ele- 

 vated above the axis, and not mucronate. 



The following figures, already given in the Geological Report on Wis- 

 consin, illustrate the species, so far as the specimens in my possession serve 

 to furnish characters. 



Dendrograptus hallianus ( Prout ) . 



a. A portion of the frond of the natural size. 



b. An enlargemen.t of one of the branchlets, showing the cellules. 



e. The main stipe and some of the principal branches, natural size. There is a swelling or 

 protuberance at the base, or radicle, one side of Avhich is brok«n off. 



This species occurs in beds somewhat above the middle of the formation, 

 at Osceola mills on the St.Croix river. 



