CRETACEOUS LAMELLIBRANCHIA. 
— 
oO 
1884. Janrra atava, O. Weerth. Die Fauna des Neocom. im Teutoburg. Walde 
(Paleont. Abhandl., vol. ii), p. 54. 
1887. = —- Ii. Mallada. Sinops. Espec. Fés. en Espana, vol. i, Cret. 
infer. (Bolet. Com. Mapa geol. Espana, 
vol. xiv), p. 129. 
— — wneocomtenstis, Mallada. Ibid., p. 130. 
1891. — apava, J. Felix.  Verstein. mexican. Jura- u. Kreide- Format. 
(Paleontographica, vol. xxxvii), p. 171. 
1895. - -- G. Maas. Zeitschr. d. deutsch. geol. Gesellsch., vol. xlvu, 
p. 269. 
1896. — — A, Wollemann. Ihbid., vol. xlvin, p. 841. 
1899. Vora (Jantra) atava, D. J. Anthula. Kreidefoss. d. Kaukasus (Beitr. z. 
Palwont. u. Geol. Osterr.-Ungarns 
u. d. Orients, vol. xii), p. 71. 
1900. Janrra atava, A. Wollemann. Die Biv. u. Gastrop. d. deutsch. u. hol- 
lind. Neocoms (Abhandl. d. k. preus- 
sisch. geol. Land., N. F., pt. 31), p. 50. 
Po Vota atava, G. Miller. Verstem. des Jura und der Kreide (Deutsch- 
Ost-Afrika, vol. vii), p. 551, pl. xxiv, fig. 4. 
2? Non 1883. Preren (Netruma) atava, W. Keeping. Foss., etc., Neoc. Upware and 
Brickhill, p. 107, pl. iv, fig. 6. 
Deseviption—Shell roughly triangular, often shghtly imequilateral; ventral 
marein very convex, with deep incisions between the main ribs; postero-dorsal 
margin concave, antero-dorsal nearly straight. Anterior ears long, triangular. 
Right valve convex, with the umbo considerably incurved and sharp. The six 
main ribs are prominent and rounded, and are separated by much broader inter- 
spaces, which are concaye or somewhat flattened. In the interspaces and on the 
sides of the main ribs, from three to twelve small, shghtly raised ribs usually 
occur, but are absent in some cases; the central ribs are rather stronger than the 
lateral. Numerous fine, equal, regularly placed, concentric ridges cross both ribs 
and interspaces ; they are parallel with the ventral margin of the valve, and con- 
sequently bend ventrally in crossing the main ribs, and curve dorsally m the inter- 
spaces. Similar concentric ridges are also present on the ears. 
Left valve flattened, sometimes shehtly convex or shghtly concave, with six 
main ribs, which are rounded and somewhat more prominent than those on the 
right valve. Interspaces broad and deep, with small ribs. Concentric ornamentation 
similar to that on the right valve. 
Measurements : 
(1) (2) (3) (4) (5) (6) (7) (8) (9) 
Length. 24 . 28 . 22 wn 5 BHO 5, BO 5 ts) . Wy . Bil waa, 
Height . 30 . 28 . 29 My 5 26 . By . Bo . 22. B87 x 
(1—8) Upware. (9) Faringdon, 
