PANOPEA. 227 



usually less distinct than iu tlie variety jjlicatK, the luuular depression is smaller 

 and shallower, the umbones broader, and the ventral margin usually more distinctly 

 curved. The smaller specimens of the var. neocomiensis resemble the example 

 figured by d'Orbigny, in which the anterior margin is obliquely truncated, and 

 a carina extends from the umbo antero-ventrally. 



In one form (Plate XXXV, fig. 10), which in other respects resembles the 

 variety neocomiensis, the anterior half of the shell is relatively more inflated, and 

 the posterior part is not so high as the anterior part ; this form may be known 

 as P. ijurgilis var. a. In addition to these forms of Z'. gwrgitis numerous other 

 modifications occur. 



Specimens from the Speeton Clay have been recorded by previous writers as 

 P. neocomiensis; the examples seen are few in number and not well preserved, 

 but resemble closely the smaller form of P. gun/if is var. neocomiensis (Plate XXXV, 

 fig. 13). In one case the fine, radial ornamentation is shown. 



Specimens from Blackdown (Plate XXXVI, figs. 6, 7) resemble the variety 

 2)lic<ifii from tlie Lower Greensand, but are somewhat less convex ; these probablv 

 constitute only a local variety, since examples from the Upper Greensand of Dorset 

 agree in convexity and in other characters with typical forms of the var. plicafu 

 from the Lower Greensand. The examples from Blackdown, although few in 

 number, show considerable variation; one specimen (Plate XXXVI, fig. 8), is 

 nuich shorter than usual, and resembles d'Orbigny's^ figure of P. pUcata, but 

 is less convex. 



Crushed internal casts of Panopea have been found in the Chalk ]\Iarl of 

 Folkestone ; they resemble P. gnrgitis var. jilicatu, but their imperfect preservation 

 renders determination difficult. 



Ti/pes. — The type of 1'. gnrgitis came from the Aptian of the Perte-dn-lihnne ; 

 that of P. neocomiensis from the Xeocomian of Aubc. The type of /'. pUcnfn 

 was obtained from the Lower (Greensand of Sandgate, but cannot now be found. 

 The type of /'. Igeviuscula, from the Upper Greensand of Blackdown, is in the 

 Bristol iluseum. 



Distriliiition. — Lower Greensand : Perna-hed, Crackers and Beds iv, vi, vii, x, 

 xiii, and xiv of Atherfield. P«-/(''-bed of Sandown. Ferruginous Sands of Slianklin. 

 Atlierfield Beds of East Shalford and Scvcnoaks. Hythe Beds of Hythe and 

 Court-at-Street. Sandgate Beds of Pai liani Park. ^[(lmnliUlJfns Bed of Folke- 

 stone. Recorded 1)V T()})ley from the Atherfield Chiy of Haslemere, Peasmarsh, 

 Redhill, aiul Hythe; from tlie Hythe Beds of Pulborough; from the Sandgate 

 Beds of Folkestone and Sandgate ; and from the Folkestone Beds of Folkestone. 

 ? Lower Greensand of L^pware. PSpceton Clay of Speeton. Gault of Black Yvu 

 and Folkestone. Upper Greensand of Blackdown and Black Ven. 



1 ' Pal. Franc. Terr. Crt't.,' vol. iii (1845), p. 337, i>\. ccclvii, figs. 4, 5. 



