43 CARBONIFEROUS CEPHALOPODA OF IRKLAND. 



generic name Oncoceras, 1 James Hall described several species from the Ordovician 

 and Silurian rocks of the State of New York. The genus was afterwards recog- 

 nised by Billings (who employed Hall's generic name) from rocks of the Niagara 

 group in Canada, and a number of species of it were described by him (' Catalogue 

 of the Silurian Fossils of Anticosti,' 1866). M'Coy, in his ' Synopsis of the Silurian 

 Fossils of Ireland,' 1846, described and figured Poterioceras approximatum from 

 Ordovician rocks, but this appears to have been a somewhat doubtful determination 

 as regards the genus. 2 



Of Silurian species of Poterioceras, Barrande described some from his Etage E, 

 among which may be mentioned P. heteroclitum (' Syst. Sil. Boh.,' vol. ii, pi. cxviii) 

 and P. lumbosum (ibid., pi. cccclxiv). 



The Devonian rocks have yielded a few species, among which may be cited 

 rthoceratites subfusiformis, Minister, 3 0. subpyriformis, Miinster, and Gomplw- 

 ceras sulcatulum, Murch. de Vera., and de Keyserl. 4 To these may be added the 

 species described by Whidborue in his valuable " Monograph of the Devonian 

 Fauna of the South of England " (Palaeont. Soc. vol. for 1889), under the names 

 Poterioceras vasiforme, P. Marri, and P. ellipsoideum. 



In the Carboniferous rocks only four species are known to me with certainty 

 as referable to Poterioceras .• these are P. cordiforme, J. Sowerby ; P. fusiforme, 

 J. de C. Sowerby; P. ventricosiim, F. M'Coy; P. latiseptatum, A. H. Foord. 

 Probably de Koninck's species, Gomplwceras fusiforme (not Sowerby's) and G. 

 lagenale also belong here. 5 



Poterioceras is nowhere very rich in species, the most numerous in any rocks 

 being those of the Ordovician and Silurian of North America. 



1 M'Coy's name Poterioceras has priority over this one, which was adopted by Hall for what he 

 uo doubt considered at the time he wrote to be a distinct genus (' Palaeont. New York,' vol. i, 1847). 



2 See Blake, 'British Foss. Ceph.,' 1882, pt. 1, pi. xxiv. 



3 'Beitrage zur Petrefactenkunde,' 1840. 



4 ' Geo), de la Russie d'Europe,' vol. ii, Palaeont. 



5 ' Faune Calc. Carb. Belg.,' torn, v, 1880. 



