

17 



The organic centre from which the cells radiate (in two 

 specimens) is elevated, and does not quite correspond with the 

 centre of the mass. The central cells are very minute, those 

 near the margin having a diameter five or six times as great. 



This species has nearly the same diameter as R. iowensis, 

 but the cells are proportionally large, and the rhomboidal ap- 

 ertures more sharply defined, while the centre is not broadly 

 depressed as in that one ; but widely and sometimes almost 

 hemispherically convex, with a slight depression on one side 

 of the organic centre. 



Geological formation and locality. In the limestone of Ra- 

 cine of the horizon of the Niagara limestone of New York. 



Collector. T. J. Hale. 



GRAPTOLITIDEiE of the Lower Silurian rocks of Wisconsin. 

 GRAPTOLITHUS (Diplograptus) peosta, Hall. 



Description. Stipe (simple ?) robust, rounded on the surface, 

 with section broad-oval ; very gradually widening from base, 

 having a width of about eight hundredths of an inch : cellules 

 narrow-elongate, about twenty-six in the space of an inch ; 

 length about three and a halt' times the width of the cell, the 

 free portion being about one-third the length ; inclined to the 

 axis at an angle of about 35°; extremities of the cells trun- 

 cate, the apertures somewhat quadrangular and rounded on the 

 sides. Cell partitions strong and well denned, reaching near- 

 ly to the centre of the stipe in its lower part, leaving a very 

 narrow space for the common body, which becomes wider above. 

 Surface transversely striated or wrinkled. 



Geological formation and locality. In the shales of the Hud- 

 son River group in Wisconsin, Iowa and Illinois. 



DICTYONEMA neenah, Hall. 



Description. Frond spreading, infundibuliform, reticulate, 

 the radiating branches slender, direct, a very little undulating, 

 the transverse connecting filaments more slender than the 

 branches; reticulations quadrangular or oval, the length from 

 one and a half to twice the width ; from six to seven and a 

 half in the space of half an inch, and transversely from twelve 

 to fourteen in the same distance. Serrations or cellules not 

 determined. 



This species is deeply funnel shaped, the branches but slight- 

 ly diverging and the intercalated or implanted branches at dis- 

 tant intervals. The matrix is a compact granular limestone, 

 2gr 



