PECTEN. 20] 
It is difficult to separate Janira Johannis Bahmi, Tiessen,' from P. (N.) cometa, - 
since in the latter the symmetry (depending on the position of the middle rib) 
varies in different specimens. 
P. (Neithea) cometa also presents some resemblance to the smaller forms of 
P. (N.) atavus, but is distinguished by possessing five (imstead of six) main ribs, 
by being relatively higher, and by having the right valve more convex. 
Remarks.—This appears to be a relatively rare species. A specimen from the 
Cenomanian of Saint Jouin (Seine-Inférieure) has been sent me by M. Fortin, and 
agrees perfectly with the English examples. 
T'ypes.—D’ Orbigny’s specimens came from the Cenomanian of Villers (Calva- 
dos) and Le Havre (Seine-Inférieure). 
Distribution.—Upper Greensand (zone of Pecten asper) of the Isle of Wight, 
Maiden Bradley, Melcombe Bingham (Dorset), south-west of Armswell Farm 
(Dorset), and west of Melbury Hill (Dorset). Rye Hill Sands of Warminster. 
Chloritic Marl of Ventnor and Maiden Bradley. Cenomanian of Wilmington. 
Pecren (Nerruva) Morrist (Pictet and Renevier), 1858. Plate XXXIX, figs. 
lla—e, 12a, b, 15. 
? 1841. Pecren Quinquecosratus, var. a, F. A. Rémer. Die Verstein. d. nord- 
deutsch. Kreidegeb., p. 54. 
1845. — = E. Forbes. Quart. Journ. Geol. Soe., vol. i, 
p. 249 (partim). 
1846. — versicostatus, A. Leymerie. Statist. géol. et min. du départ. de 
lAube, Atlas, p. 11, pl. vi, fig. 9. 
1847. — QuINQUECosTaTUS, var., J. Morris. Quart. Journ. Geol. Soc., 
vol. 11, p. 295 (foot-note) 
1853. Janrra quinquecosrata, F. J. Pictet and W. Roux. Moll. Foss. Grés verts 
de Gentve, p. 506, pl. xlv, 
figs. 3a, b (not c). 
1858. — Morxrtsr, Ff’. J. Pictet and EB. Renevier. Foss. Terr. Aptien (Matcr. 
Pal. Suisse, ser. 1), p. 128, 
pl. xix, fig. 2. 
? 1859. guinquecosrata, J. Vilanova y Piera. Mem. geogu.-agric. de Cas- 
tellon, pl. iii, fig. 23. 
1865. — Morrisi, H. Coguand. Mon. Aptien de l’Espagne, p. 151. 
1870. _— -- F. J. Pictet and G. Campiche. Foss. Terr. Crét. Ste. 
Croix (Matér. Pal. Suisse, ser. 5), p. 244. 
1887. -- — L. Mallada. Sinops. Espec. Fos. Espana, vol. ii, Cret. 
infer. (Bolet. Com. Mapa geol. Espana, 
vol. xiv), p. 130. 
' « Zeitschr. d. deutsch. geol. Gesellsch.,’ vol. xlvii (1895), p. 473, pl. xvii, fig. 5. 
