6 CRETACEOUS LAMELLTBRANCHIA. 



Description. — Shell thin, greatly elongated, compressed ; the anterior part 

 short and rounded ; the posterior part very long and tapering, with a slight carina 

 extending from the umbo to the postero-ventral angle, cutting off a flattened 

 area. Umbones small. Ventral margin slightly sinuous posteriorly (except in 

 young specimens, in which the posterior part of the valve is less produced) ; 

 postero-dorsal nearly straight. Posterior margin truncated. Surface glossy, with 

 very fine concentric lines. Margin entire. Teeth very numerous, minute, short. 

 Adductor impressions faintly marked. 



Measurements : 



(1) (2) (3) (4) 



Length . 26 . 20 . 14 . 10 mm. 



Height . 9 . 7 5 4 „ 



Affinities. — N. solea is more elongated than any other Cretaceous species here 

 described (see page 1). 



Types. — I have not seen the type ; it appears to be missing from the 

 d'Orbigny Collection in the Museum of Natural History, Paris. Gardner's 

 specimens are in the British Museum. 



Distribution. — Lower Gault (zones ii, iii, v, vii) of Folkestone ; Gault of 

 Black Ven ; Cambridge Greensand {fide Price). 



Nuculana Marine (oVOrbigny), 1844. Plate I, figs. 25 a—c, 26 a, b, 27. 



1814. Nttcula MAiuiE, A. d'Orbu/ny. Pal. Fran?. Terr. Cret., vol. iii, p. 169, 



pi. ccci, figs. 4—6. 

 1850. Leda Mabi;e, A. d'Orligny. Prodr. de Pal., vol. ii, p. 136. 

 1866. — — F.J. Pictet and Q. Campiche. Poss. du Terr. Cret. de Ste. 



Croix (Mater. Pal. Suisse, ser. 4), pt. 3, 

 pp. 397, 401. 

 1884. — — J. S. Gardner. Quart. Journ. Geol. Soc, vol. xl, p. 138, 



pi. iii, figs. 28, 29. 



Description. — Shell elongated, inequilateral. Ventral margin considerably and 

 evenly curved ; antero-dorsal straight or slightly convex, postero-dorsal slightly 

 concave, both with a considerable ventral slope. Anterior end blunt and rounded ; 

 posterior end pointed. Posterior part of shell more compressed than the median 

 and anterior portions. Umbones pointed. Surface ornamented with numerous 

 fine, concentric ribs, which are absent or indistinct on the anterior and posterior 

 parts of the valves. Anterior teeth about thirteen, posterior more. 



Measurements : 









Length 



(i) 

 8 



(2) 



7 



(3) 



. 4 mm. 



Height . 



5 



4 



. 3 „ 



Thickness 



3-5 . 



— 



55 



