PLICATULA. 141 



of the same. He admits, however, that P. Cotteaui is practically inseparable from 

 P. radiola, d'Orbigny, and gives the name chiefly because it occurs on a different 

 horizon. Peron considers that P. Cotteaui is distinct from P. injlata : after the 

 examination of a large series of specimens of different ages I am unable to accept 

 that view, especially in consideration of the large amount of variation which occurs 

 in the very closely allied species P. gurgitis. P. injlata is distinguished from 

 P. gurgitis by the fewer and more regular ribs and the fewer spines ; also by the 

 ribs being absent or indistinct on the ventral part of the valves in large specimens. 

 Some specimens of P. injlata, with more numerous ribs, approximate to certain 

 examples of P. gurgitis which have fewer ribs than usual; this is more particularly 

 seen in some examples from the Upper G-reensand. 



Remarks. — The number and strength of the ribs vary in different examples ; 

 large specimens are sometimes almost smooth {e.g. PI. XXVI, fig. 9). 



Since two forms were included by Lamarck under the name P. radiola, and 

 since uncertainty exists as to which of them his name should be applied to, I follow 

 Pictet, Renevier, and Campiche in retaining the name injlata given by Sowerby. 



Types. — P. injlata is from the Cenomanian near Cambridge ; the specimens 

 cannot now be found. The type of P. spinosa, Mantell, is in the British Museum. 



Distribution. — Upper Greensand near Nursted and (Chert Series) of the Isle 

 of Wight. Rye Hill Sand of Warminster. Chloritic Marl of Maiden Bradley and 

 the Isle of Wight. Grey Chalk of Folkestone. Chalk Marl of Ventnor, Folkestone, 

 Reach, Burwell, Haslingfield, Harlton, Speeton, etc. Zone of HoJaster suhglohosns 

 of Hitchin, Totternhoe, Arlsey, Isleham, Burwell, Cherry Hinton, Fulbourn, 

 Shelford, Louth, Withcall, Speeton, etc. 



I have seen no examples from the English Lower Cretaceous which could be 

 definitely referred to this species, but Topley (1875) has recorded P. injlata from 

 the Hythe and the Sandgate Beds. 



Plicatula Bareoisi, Peron, 1887. Plate XXVI, figs. 12—18. 



1846. Plicatula pectinoides, A. E. Reuas (non Sowerhij). Die Yerstein. der 



bohrn. Kreideformat., pt. ii, p. 37, pi. xxxi, 

 figs. 16, 17. 

 1850. — NODOSA, A. d'Orhigny. Prodr. de Pal., vol. ii, p. 254 (partim). 



1872. — — H. B. Geinitz. Das Elbthalgeb. in Sachsen (Palteou- 



tographica, vol. xx), pt. ii, p. 32, 

 pi. ix, fig. 5. 

 1878. — — C. Barrois. Terr. Crut. des Ardoimes (Ann. Soc. 



geol. Nord, vol. v), p. 391. 



