256 
NATJTILOIDEA. 
Family POTERIOCEEATID^ 
Genus POTERIOCER AS, M‘Coy 
{Orthocera (pars), J. de Carle Sowerby, 1829^; Ortlioceras (pars), 
Phillips, 1836 ^ ; Gomphoceras (pars), Munster, 1840®; Kelimenia, 
telnau, 1843 Gomphoceras, Murchison, Yerneuil, and Keyserling, 1845'’’; 
Ooicoceras, Hall, 1847 ® ; Gomphoceras, d’Orhigny, 1849 ® ; Gomphoceras, 
S. P. Woodward, 1851 Phragmoceras, Geimiz, 1853 ; ? Gomphoceras 
(pars), Eichwald, 1860 ■ Phragmoceras, Eichwald, 1860 ; Cgrtoceras, 
Billings, 1863 ; Gomphoceras (pars), Barrande, 1867 ; Cyrtoceras 
(pars), Barrande ^®.) 
Gen. Char. Shell fusiform, slightly curved, very slender in the 
apical portion and becoming inflated in the middle, and contracting 
again towards the aperture, which is simple. Cross section nearly 
circular in the young, elliptical in the adult. Siphuncle subcentral 
to marginal, much inflated between the septa ; the latter somewhat 
distant from each other, and oblique to the long axis of the shell. 
Body-chamber large in proportion to the entire shell ; constricted 
near the aperture. Shell smooth in all the known species. 
Remarks. This genus may be distinguished from Gomphoceras, 
with which many authors have confounded it, by its simple aperture 
and fusiform shape, and from Cyrtoceras by the inflation of the 
central portion of the shell, and its contraction in the region of the 
aperture. It is to be noted that the inflation is much less conspi- 
cuous in the adult than it is in the young. 
^ This name is proposed in substitution for that of Oncoceratidce institu^^ed 
by Hyatt (Proc. Boston Soc. Hat. Hist. vol. xxii. 1883, p. 282), and it includes 
the following genera: — Eremoceras, Hyatt, type Cyrtoceras Syphax, Billings 
(Pal. Foss. vol. i. p. 194, f. 178) ; Clinoceras, Mascke (Zeit. d. deutsch. geol. 
Gesell, Band xxviii. p. 49) ; Poterioceras, M'Coy (Synop. Carb. Foss. Ireland, 
1844, p. 6). Only the last-named genus is represented in the National Collection. 
2 Loc. cit. 
3 Min. Conch, vol. vi. p. 167, tab. dlxxxviii. f. 1 (not f. 2). 
^ Geol. of Yorkshire, pt. ii. p. 238 [0. fusif or me). 
® Beitrage z. Petrefact. Heft iii. pp. 103, 105. 
® Syst. Sil. de I’Amerique Septentrionale, p. 33. 
’’’ Geol. de la Eussie d’Europe, vol. ii. Palaiont. p. 357. 
® Pal. of Hew York, vol. i. p. 197. 
® Prodr. de Paleont. Stratigr. vol. i. p. 112. 
Manual of the Mollusca, p. 90. 
Die Yerstein. d. grauw. Form, in Sachsen, Heft ii. p. 33. 
Lethsea Eossica, vol. i. Seconde Sect, de I’ancienne Periode, p. 1269. 
13 Pid. p. 1272. 
11 Geol. of Canada, Appendix, p. 951. 
15 Syst. SiL de la Boheme, vol. ii. pt. i. p. 243. 
1® Ibid. p. 550 (C. heteroclytum). 
