452 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Lower Carboniferous Rocks. The genus Argus seems to be the same as 
Dithyrocaris, although Salter does not express that opinion. Fig. 69° rep- 
resents Argus testudineus ; the surface of the body is striated. Dithy- 
rocaris pholadomyia Salter had a carapace 7 inches long. The genus 
Argus of Scouler is apparently the same as Dithyrocaris. 
D. tenuistriatus McCoy, Woodward, Geol. Mag. viii. Great Britain. 
D. belli Woodw. 1. c. Devonian, Gaspé, Canada. 
D. Neptuni Hall (Fig. 73), 16th Ann. Rep. State Cabinet, N. York. 75, Pl. I, fig. 9, 1863. 
Hamilton group, Devonian of New York. 
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Fig. 73.—Dithyrocaris neptuni Hall; telson and cercopoda, natural size. From Hall. 
Hall’s figure was made from a cast, no restoration having been at- 
tempted. From the size of the telson and the cercopods, it is evident 
that the animal must have been enormous, perhaps between two and 
three feet in length. 
Genus RuacHuRA Scudder, 1878. 
R. venosa Scudd., Proc. Bost. Soc. Nat. Hist. XIX, 296. Pl. 9, fig. 3, 3a. March, 
1878. Coal measures, Danville, Ohio. 
