10 CRETACEOUS LAMELLIBRANCHIA. 



Nuculana Vibrayeana (d'Orbigny), 1844. Plate II, figs. 4 a — c, 5 a, b, 6 — 9. 



1844. Nucula Vibeateana, A. di'Orbigny. Pal. Franc. Terr. Cret., vol. iii, 



p. 172, pi. ccci, figs. 12—14. 

 1850. Leda Vibeateana, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 136. 

 1852. Nucula Vibeateana, F. J. Pictet and W. Roux. Moll. foss. Gres vert 



de Geneve, p. 471, pi. xxxix, fig. 2. 

 1861. — subelliptica, R. G. Seeley. Ann. Mag. Nat. Hist., ser. 3, 



vol. vii, p. 120, pi. vi, fig. 4. 

 1861. — euomboidea, Seeley. Ibid., p. 120, pi. vi, fig. 5. 

 1866. Leda Vibeateana, F. J. Pictet and G. Campiche. Foss. Terr. Cret. de 



Ste. Croix (Mater. Pal. Suisse, ser. 4), 



pt. 3, pp. 399, 401, pi. cxxix, figs. 5, 6. 



1884. — — J. S. Gardner. Quart. Journ. Geol. Soc, vol. xl, 



p. 137, pi. iii, figs. 17, 18, 25 ; pi. iv, figs. 

 26, 27. 



Description. — Shell oval, rounded, convex centrally, compressed at the extre- 

 mities, nearly equilateral, but with the posterior part slightly longer than the 

 anterior ; extremities rounded. Ventral margin considerably curved at the median 

 part. Antero-dorsal and postero-dorsal margins with a considerable ventral 

 slope from the umbo. Umbones not prominent. Lunule indistinct. Escutcheon 

 lanceolate. Surface smooth. Margins smooth. Anterior adductor impression 

 somewhat quadrate ; the posterior a little smaller and more rounded. Pallial 

 line slightly sinuous posteriorly. 



Measurements : 

















Length 



(i) 

 15 



(2) 



13 



(3) 

 11 



(4) 

 11 . 



(5) 



10 



(6) 



. 9 . 



(7) 



6*5 mm 



Height 



12 



10 



8 



9 . 



8 



7 . 



5-5 „ 



Thickness . 



8 



6 



6 



5-5. 



5 



. 4-5 



3 „ 



Affinities. — See under N. Seeley i, Gardner (p. 5). 



Remarks. — As was pointed out by Gardner, Seeley's N. subelliptica (PI. II, 

 fig. 9), and N. rhomboidea from the Cambridge Greensand, are simply internal 

 casts of N. Vibrayeana. 



Types. — I was unable to find the type in the d'Orbigny Collection at the 

 Museum of Natural History, Paris. The types of N. subelliptica, Seeley, and 

 N. rhomboidea, Seeley, are in the Woodwardian Museum, Cambridge. The 

 examples figured by Gardner are in the British Museum. 



Distribution. — Lower Gault (zones v, vii, and viii) of Folkestone; Cambridge 

 Greensand (derived). 



