PANOPBA. 225 



Panopea, but l:)y some to Plenrouiija.^ 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 Panopm (Plate 

 XXXVI, fig. G); and a well-developed, broad, external ligament is present (Plate 

 XXXV, figs. 9 i, 1 1 h). The fine radial ornamentation (Plate XXXV, figs. 9 c, 13 //) 

 agrees perfectly with that found in Tertiary species of Panojjea.'' 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 Panopen. 



Pictet and Renevier thought that P. pUratit (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 ])y the possession of strong concentric folds and by the absence of fine radial 

 ornamentation. But when iiumerous 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. rtcocomiensix, but these features are now known 

 to be inconstant. It appears, therefore, that there is no character by which P. 

 pHcala can be separated from P. neocomiensis. 



It is evident from Brongniart's remarks that his specimens of Lntrnriu gurgitis 

 came from the Perte-du- Rhone. 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. plica ta. Since these two forms are now united it follows 

 that the earlier name given by Brongniart should be used for this species. Later 

 writers liiive unfortunately used the name gm-gHis for a species from the Chalk. 



P. acutisulcatd (Deshayes'') and P. Srhri'xJi'ri (^Yollemann^) appear to be closely 

 allied to P. gin-gifis. 



1 For au accouiit of tho characters of this wenus see Terqueni, ' Bull. Soc. geol. cle France,' ser. 3, 

 Vol. X (1853), p. 634, and " Observations sur les Etudes critiques des MoUusques Fossiles compreuaut 

 la monographie des Myaires de M. Agassiz," ' Mem. Acad. Imp. de Metz,' aimce 1854 — 55 (1855), p. 253. 



- See, for instance, P. intermedin (Sow.) from the London Clay, etc., and P. //orirfrtHot, Heilprin, 

 from the Caloosaliatchie Beds of Florida. '^ ' Terr. Cret. Ste. Croix ' (18G5), p. 51. 



' ' Foss. Terr. Aptieu ' (• Mater. Pal. Suisse,' ser. 1, 1855), pp. 56 (footnote), 175. 



5 Leymerie, ' Mcui. Soc. geol. de France,' ser. 2, vol. v (1842), p. 3, pi. iii, fig. 2; d'Orbigny, 

 ' Pal. Franc. Terr. Cn't.,' vol. iii (1845), p. 336, pi. ccclvii, figs. 1—3 : Pictet and Campiche, 'Terr. 

 Crct. Ste. Croix" (' Mater. Pal. Suisse,' ser. 4, 1865), p. 65. 



" ' Die Biv. u. Gastmp. il. (Umtscli. u. holliind. Neocoms ' (' Abhandl. d. k. preussisch. geol. Laud., 

 N. F., pt. 31, 1900), p. 126. pi. v, fig. 7. 



30 



