of North America with those of Europe. 223 



The Lichas scabra of Bohemia belongs, according to Mr. 

 Barrande, to the lowest beds of the upper stage of the Silurian 

 system, while the Lichas laciniata of Sweden^s found, like that 

 of America, in the lower stage. We have seen in the collections 

 °l ^ r * •*• Hall, at Albany, a specimen very much like that of 

 Cincinnati, coming from the Trenton limestone. 



Ceraurus pleurexanthemas, Green. — In comparing the frag- 

 ments of the head which I possess, of this species with the Chei- 

 rurus exsul, Beyrich, I have not been able to discover any 

 difference. This author, like ourselves, knew only of the head 

 of the Cheirurus exsul, which has been found in the bowl- 

 ders of limestone coming from Scandinavia, and containing the 

 most characteristic trilobites of the lower stage of the Silurian 

 system, such as the Asaphus expansus and Illamus crassicanda. 

 The Amphion gelasinosus, Portlock, of which this author has 

 seen only the head, and which appears also to be the same 

 species, belongs to the lower Silurian beds of Ireland. The 

 C er minis pleurexanthemus characterizes also the same stage in 

 America. We have found it at Middleville, N. Y., in the Tren- 

 ton limestone, and at Galena, Illinois, in the blue limestone. Mr. 

 13. Dale Owen says he has found it at Cincinnati in beds of the 

 same age.* 



Trinucleus caractaci, Murch. — This species is abundant in 

 America, chiefly in the Hudson River group of the State of Sew 

 York. It occurs also in the blue limestone of Cincinnati, and of 

 Newport, in Kentucky. According to Prof. Emmons, the T. tes- 

 sellatus, Green, very abundant in the lower beds, that is to say, 

 w the Trenton limestone at Sackets Harbor, at Glens Falls, 

 N. Y., and at Montreal, is distinguished from the T. caractaci 

 by the shorter spiniform prolongations, by the narrower perforated 

 limb, and by the number of perfect circles of perforations which 

 Would be three instead of four.f The T. caractaci belongs in 

 •Europe to the middle and upper region of the lower Silurian 

 stage, and is found principally in the sandstone of Caradoc. All 

 the species of Trinucleus are in general proper to the lower stage 

 of the Silurian system. We know no exception to this rule in 

 America, and we know only one in Europe.;}: 



Phacops Hausmanni, Brongn.,sp. — This species, in Bohemia, 

 proper to the higher and middle divisions, appears in America in 

 exactly the same position, that is to say, ill the Pentamerus gale- 



* [This peculiar and well marked species is evidently identical with the Ckeiru- 

 r*s exsul and Ampkion gcfasinosus cited above, and also with Calymerut speciosus, 

 Salman. It is also closely allied, or identical with several other European species 

 which have been described from fragments. (Sea Pal. N. V., vol. i, p. 312.)— J. H.] 



'Mr. Hall thinks, nevertheless, that the T. tessellaius and T. caractaci should 

 b * united. [See Pal. N. Y., vol. i ? p. 249.] 



♦ ll is said that Trinucleus has lately been found in the slates of Weniock. 



