(4) 



(5) 



12-5 . 



9 



11 



7-5 



— . 



4-5 



LUCINA. 155 



Ornamentation consists of numerous, regular, strong, concentric ribs which become 

 smaller near the antero-dorsal and postero-dorsal margins. 

 Measurements : 



(1) (2) (3) 



Length 15 . 14 . 13 



Height 14 . 12 . 11 



Thickness 8 7 6-5 . 



(1 — 5) Gault, Folkestone. 



Affinities. — In form and ornamentation this species resembles L. Sanctse-Grucis, 

 Pictet and Campiche, 1 but is much smaller and relatively longer. 



Type. — The type came from the Gault of Folkestone, but cannot now be 

 found. The specimens figured by Jukes-Browne are in the Sedgwick Museum, 

 Cambridge. 



Distribution. — Gault of Folkestone and Black Ven. Cambridge Greensand. 

 Upper Greensand (zone of Schlcenbachia rostrata) of Devizes. 



Lucina DowNEsr, sp. nov. Plate XXIV, figs. 15 a — c. 



Description. — Shell oval or nearly orbicular, moderately convex, slightly inequi- 

 lateral, longer than high, postero-dorsal part compressed. Anterior and ventral 

 margins rounded. Posterior margin less convex than the anterior, forming an 

 obtuse angle with the convex postero-dorsal margin. Umbones of moderate size. 

 Lunule elongate. Ornamentation consists of numerous regular, concentric, lamellar 

 ribs separated by broad, flat interspaces with fine concentric ribs. 

 Measurements : 



(i) (2) 



Length . 32 . 2G mm. 



Height . 28-5 . 24 „ 

 Thickness . 14 . — ,, 



(1, 2) Blackdowii. 



Affinities. — This species resembles L. Comueliana, d'Orbigny, 2 from the 

 Neoconiian, but the umbones are less prominent and the shell is less inequilateral. 

 It is also similar to L. subiiumismalis, d'Orbigny, 3 from the Aachen Greensand, 

 but the ribs are more numerous and the antero-dorsal margin has a greater 



1 " Terr. Crct, Ste. Croix " (' Mater. Pal. Suisse,' ser. 4, 1866), p. 289, pi. exxii, fig. 8. 



2 'Pal. Franc. Terr. Cret,,' vol. iii (1844), p. 116, pi. eclxxxi, figs. 3—5. 



3 Holzapfel, "Die Mollusk. Aachen. Kreide " (' Palaeontographica,' vol. xxxv, 1880), p. 187, 

 pi. xix. figs. 1 — 3. Eavn, 'Mollusk. i Danmarks Kridtafl. I. Lamellibr.' (1902), p. 129, pi. iv, 

 fie. -21. 



