OG CRETACEOUS LAMELLIBRANCHIA. 



Distrihiifion. — Greensand of Blackdown. Greensand (chert beds) of Woodlands 

 Covert, Great Haldon. Upper Greensand of Black Ven and Devizes. Cenomanian 

 (Meyer's Bed 12) of Dunscombe. ? Gault of Black Ven. 



MoDioLA LiGERiENSis (tV Ovbignij), 1844. Plate XVI, figs. 4 a, h, ba, b, 6. 



1844. Mttilus ligeeiensis, A. d'Orbii/ny. Pal. Fran9. Terr. Cret., vol. iii, 



p. 274, pi. cccxl, figs. 1, 2. 

 1850. — — — Prodr. de Pal., vol. ii, p. 165. 



1867. — — U. Gueramjer. Album Palcout. de la Sarthe, p. 17, 



pi. xxii, figs. 2 — 4. 

 1867. MoDiOLA LIGEEIENSIS, -F. /. Pictet and G. Cavipiche. Foss. Terr. Cret. Ste. 



Croix (Mater. Pal. Suisse, ser. 4), p. 509. 

 ? 1876. — — D. Brauns. Zeitschr. f. d. gesammt. Naturwiss., 



vol. xlvi, p. 374. 

 ? 1883. — TYPiCA, A. Fritsch. Stud, im Gebiete der bolim. Kreideformat., 



iii. Die Iserschichten, p. 106, fig. 73. 



? Non 1846. Mytilus (Modiola) ligeeiensis, A. E. Eeuss. Die Verstein. der bohm. 



Kreideformat., pt. 2, p. 16, pi. xxxiii, 



fiff. 3. 



Measareiiieuts 



(1) (2) 



Leng-th 89 . . 60 mm. 



O" 



Greatest height (perpendicular to 



length) 40 . . 25 „ 



Thickness . . . . . 34 . . 24 „ 

 (1) aud (2) from the Perna-hed of Atherfield. 



Affinities. — This species agrees with M. reversa, Sowerby, and seems to be 

 distinguished only by the crimp-like ornament in the spaces between the ribs ; this 

 is usually best developed on the dorsal and postero-ventral parts of the valves, and 

 seems always to be absent on the anterior region. The specimens of 31. recersa 

 from Blackdown do not show that ornament,^ and its absence can scarcely be 

 explained by imperfect preservation, since other finer ornament is clearly shown on 

 some specimens. On the other hand, the possibility of the two species being 

 identical is supported by the great variability in the development of the crimp -like 

 ornament in M. Ugeriensis. On some specimens from the Cenomanian of Orbiquet 

 it is very faint, but on one from Le Mans (preserved in the Ecole des Mines, Paris) 

 the crimp-ornament is stronger and more continuous than the concentric ornament. 

 ' Que speeimen seouis to show a very faiut trace of it near the hiuge-margin. 



