PANOPEA. 225 
Panopea, but by some to Plewromya.! There seems now to be sufficient evidence 
to show that it belongs to the former rather than the latter, since the hinge-margins 
of the two valves are alike and there is no overlap of left by the right margin ; 
the hinge possesses the prominent, conical tooth characteristic of Panopea (Plate 
XXXVI, fig. 6); and a well-developed, broad, external ligament is present (Plate 
XXXV, figs.9b, 116). The fine radial ornamentation (Plate XXXV, figs. 9¢, 13 d) 
agrees perfectly with that found in Tertiary species of Panopea.? I have not seen 
the hinge in any specimen from the Lower Greensand, but it is well preserved in 
a left valve from Blackdown. Pictet and Campiche’® state that casts from the Aptian 
show clearly the presence of the teeth of Panopea. 
Pictet and Renevier thought that P. plicata (Sowerby) and P. neocomiensis 
(Leymerie) should be united as one species; Pictet and Campiche, however, in a 
later work regarded them as distinct, and stated that the former differs from the 
latter by the possession of strong concentric folds and by the absence of fine radial 
ornamentation. But when numerous specimens are examined all stages in the 
strength of the folds can be seen; and those with well-developed folds show, when 
the surface is well-preserved, the same kind of radial ornamentation that occurs on 
specimens with indistinct folds. The presence of a carina in front of the umbones 
and the somewhat smaller height of the posterior part of the shell have also been 
mentioned as characteristic of P. neocomiensis, but these features are now known 
to be inconstant. It appears, therefore, that there is no character by which P. 
plicata can be separated from P. neocomiensis. 
It is evident from Brongniart’s remarks that his specimens of Lutraria guigitis 
came from the Perte-du-Rhéne. — Pictet and Renevier,* who had seen the type of 
that species in the collection of M. Deluc, recognised it as a specimen from the 
Aptian of the Perte-du-Rhone, and state that it is certainly an example of either 
P. neocomiensis or P. plicata. Since these two forms are now united it follows 
that the earlier name given by Brongniart should be used for this species. Later 
writers have unfortunately used the name quiyitis for a species from the Chalk. 
P. acutisulcata (Deshayes’) and P. Schrdderi (Wollemann’) appear to be closely 
allied to P. guigitis. 
1 For an account of the characters of this genus see Terquem, ‘ Bull. Soc. géol. de France,’ ser. 3, 
vol. x (1853), p. 534, and “ Observations sur les Etudes critiques des Mollusques Fossiles comprenant 
la monographie des Myaires de M. Agassiz,” ‘Mém. Acad. Imp. de Metz,’ année 1854—55 (1855), p. 253. 
2 See, for instance, P. intermedia (Sow.) from the London Clay, ete., and P. floridana, Heilprin, 
from the Caloosahatchie Beds of Florida. 3 «Terr. Cret. Ste. Croix’ (1865), p. 51. 
t « Foss. Terr. Aptien’ (‘ Matér. Pal. Suisse,’ ser. 1, 1855), pp. 56 (footnote), 175. 
5 Leymerie, ‘Mém. Soc. geéol. de France,’ ser. 2, vol. v (1842), p. 3, pl. ii, fig. 2; d’Orbigny, 
‘Pal. Franc. Terr. Crét.,’ vol. 111 (1845), p. 336, pl. ecclvu, figs. 1—3; Pictet and Campiche, ‘Terr. 
Crét. Ste. Croix’ (‘ Matér. Pal. Suisse,’ ser. 4, 1865), p. 65. 
6 «Die Biv. u. Gastrop. d. deutsch, u. holland. Neocoms’ (‘Abhandl. d. k. preussisch. geol. Land., 
INE EY, pt. ol, 1900); p. 126; ply ve figs, 7. 
30 
