^2 NEW YORK STATE MUSEUM 



Diplograptus peosta Hall 



Plate 25, figure 17 



Graptolithus pristis (parte) Hall. Pal. N. Y. 1847. 1:72, fig. if, ig 

 Graptolithus (Diplograptus) peosta Hall. Sup't Geol. Sur. Wis. Rep't. 



1861. p. 17 

 Diplograptus peosta Hall. Geol. Wis. 1862. 1:430 

 cf. Diplograptus ampl exicaulis James. Amer. Geol. 1889. 4:237 

 cf. Diplograptus amplexicaule AValcott. Geol. Soc. Am. Bui. 1890. 1:339 

 Diplograptus peosta Gurley. Jour. Geol. 1896. 4:298 

 Diplograptus peosta Whitfield. Amer. Mus. Nat. Hist. Mem. 2. 1895. p. 47, 



pi. 5, fig. 12 

 cf. Diplograptus pristis Winchell & Sehuchert. Geol. Minn. v. 3, pt 1, Pal. 



1897. p. 81, fig. 2 

 Diplograptus amplexieaulis Whitfield & Hovey (parte). Amer. Mus. Xat. 



Hist. Bui. v. 11, pt 1. 1898. p. 20-21 

 Diplograptus amplexieaulis Ruedemann (parte). N. Y. State Mus. Bui. 42. 



1901. p. 561 

 Hall's original description of this species is : 



Stipe (simple ?) robust, rounded on the surface, with section broad 

 oval ; very gradually widening from base, having a width of about s IOO inch ; 

 cellules narrow elongate, about 26 in the space of an inch ; length about 

 three and a half 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° ; extremi- 

 ties of the cells truncate, the apertures somewhat quadrangular and rounded 

 on the sides. Cell partitions strong and well defined, reaching nearly 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 Hudson River 

 group in Wisconsin, Iowa and Illinois. 



We reproduce here a camera drawing of a plastically preserved speci- 

 men (internal cast without periderm) from Maquoketa creek, which is con- 

 tained in the Hall collection in the American Museum of Natural History 

 and labeled there as Hall's type of I), peosta. It well bears out in its 

 characters and dimensions Hall's careful description. Besides I have before 

 me specimens in the identical state of preservation and from a like calcare- 

 ous shale of the Diplograptus bed in Graf, Iowa, and many others in com- 



