POTEEIOCEEATIDJ3. 
257 
Poterioceras makes its first appearance in the Ordovician (P. cor- 
strictum. Hall, sp.) ; then it is met with in the Silurian, in well- 
marked forms (P. heteroclytum, Barrande, spd, Syst. Sil. vol. ii. 
Fig. 45. 
Poterioceras constrictum (after Hall). — a, view of the concave side of an imper- 
fect specimen ; h, lateral view of the same, showing the constriction below 
the body-chamber, aperture imperfect ; c, transverse section of the lower 
extremity, showing siphuncle ; d, diagram of Poterioceras fusiforme, much 
reduced ; e, transverse section, showing siphuncle. 
pi. cxviii. ; P. limiboswn, Barr, sp., ibid. pi. cccclxiv.). Next it 
occurs in the Devonian under the generic names of Oomphoceras 
and Phrctfjmoceras (see ante, p. 215), enlminating in the Carboni- 
ferous, where it is rexmesented by species of remarkable size (P. 
fusiforme, J. de C. Sowerby, sp.). 
OEDOYICIAN SPECIES. 
Poterioceras approximatum, M‘Coy. 
1843. Gomphoceras suhfusiforme ?, Portlock, Geol. of Londonderry, &c. 
p. 381, pi. xxiv. f. 5 (not of Miinster). 
1846. Poterioceras cqoproxmiatum, M^Coy, Synop. Sil. Foss, of Ireland, 
p. 10, pi. i. f. 5. 
1851. Cyrtoceras, sp., Salter, Quart. Joiirn. Geol. Soc. vol. vii. p. 173, 
pi. X. f. 8. 
1854. Pkraymoceras approximatuniy Morris, Cat. of British Foss. 2nd 
ed. p. 312. 
1882. Poterioceras (?) approximatum, Blake, British Foss. Ceph. pt. i. 
p. 186, pi. xxiv. f. 6, and the figure copied from M^Coy but not 
, numbered. 
^ Fide Hyatt, Proc. Boston Soc. Nat. Hist. 1883, p. 282. P. \_Oncoc.'] Teucer, 
Bill., and P. [Owcoc.] Pettiti, Bill., from the Niagara Group of Ontario, may 
also be cited {vide Cat. Sil, Foss. Anticosti, 1866, p. 86), 
S 
