RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 41 



I 



Cheirurus nuperus Billings. 

 Cheirurus nuperus Billings, Cat. Silurian fossils Anticosti, 1866, p. 60, f. 20. 



This species was described from an isolated glabella and pygidium 

 from Div. 3 at East Point, Anticosti. Schuchert and Twenhofel have 

 listed it with a query from the upper part (D9) of their Gun River 

 formation, where it is associated with Bilobites hilohus and Triplecia 

 ortoni, in strata of Clinton age. 



Like Ch. hydei, this species shows the Cheirurus type of basal lobes 

 on the glabella and the pygidium shows three pairs of spines. The 

 outer pair or great spines are large, flat and not so long or so much 

 curved as in most of the species of the genus. C. hydei has the great 

 spines much more slender and further apart than in C. nuperiis. 



The type of this species is lost, and no further specimens have been 

 described. 



Sphaerexochus romingeri Hall. 



S-phaerexochus romingeri Hall, 20th Rept. N. Y. state cab. nat. hist., 1868, 

 p. 375, pi. 21, f. 4-7. (See Weller, Bull. Chicago acad. sci., 1907, no. 4, 

 pt. 2, p. 209, for earher and later references to this species). 



This is an exceedingly common species in the Niagaran in the 

 Chicago and Wisconsin areas but the pygidium is rare and usually 

 incorrectly figured. Hall started the misrepresentation figuring the 

 pygidium as having three spines on each side and a rounded projection 

 at the back. 



As a matter of fact, the margin of the pygidium is entire, and the 

 spines figured by Hall are the ribs on the pleural lobes. Weller 

 produced practically a similar figure, and one of Kindle's is about 

 the same, but the other, being of a mould, is more correct. Other 

 describers of the species have refrained from figuring the pygidium. 



