394 CRETACEOUS LAMELLIBRANCHIA. 



all cases, a very minute surface of attachment ; on each side of the umbo is a 

 wing-like or ear-like extension. The early part of the shell is smooth except for 

 concentric lines or ridges and occasionally fine radial furrows ; in the adult the 

 anterior and ventral marginal parts develop broad rounded folds. The stage at 

 which the folding begins and the size and number of the folds, vary in different 

 individuals. Small folds sometimes occur on the posterior wing-like part. The 

 ligament-pit is sometimes straight but usually curves posteriorly. 



Right valve at first smooth and nearly flat, occasionally slightly concave, but 

 afterwards becoming folded like the left valve. Umbo very small. 



Affinities. — Most writers, following the example of Coquand, have united 

 0. lunata, Nilsson, with 0. ungulata (Schlotheim), 1 regarding the former as a 

 young stage of the latter. Hennig (1894, 1897) and Vogel (1895), however, do not 



1 Knorr, ' Recueil. Monuin. Castast, Petrificat.,' vol. ii (1768), p. 130, P. II, pi. Dvii, figs. 5, 6. 

 Bruguiere, 'Hist. uat. Vers et Mollusques (Eiicycl. method.), Planches,' vol. iv (1827), pi. clxxxviii, 

 figs. 4, 5. Faujas-St.-Fond, 'Hist. uat. Mte. Ste. Pierre ' (1799), p. 150, pi. xxiii, fig. 6. Ostracites 

 ungulatus, v. Schlotheim, in Leonhard's ' Taschenb. fur Min.,' vol. vii, pt. 1 (1813), p. 112 ; 0. crista 

 meleagris, Schlothem, ibid., p. 112. 0. larva, Lamarck, ' Animaux sans Vert.,' vol. vi (1819), p. 216 ; 

 O. doridella, Lamarck, ibid., p. 210. ? 0. falcata, Morton, ' Amer. Journ. Sci.,' vol. xvii (1830), 

 p. 284; vol. xviii (1830), pi. iii, figs. 19, 20. O. larva, Goldfuss, ' Petref. Germ.,' vol. ii (1833), p. 10, 

 pi. Ixxv, fig. 1. ? O. falcata, Morton, ' Synop. Org. Rem. Cret. U. States' (1834), p. 50, pi. iii, fig. 5. 

 Alectryonia acrodonte, Fischer de Waldheim, 'Bull. Soc. Imp. Nat. Moscou,' vol. viii (1834 — 5), 

 p. 116, pi. v, fig. 2. O. larva, d'Orbigny, ' Pal. Franc. Terr. Oct.,' vol. iii (1847), p. 740, pi. cccclxxxvi, 

 figs. 4, 5, 8 (? 6, 7). O. larva, Midler, ' Petref. der Aachen. Kreidef ,' pt. 1 (1847), p. 39. O. tegulanea, 

 Forbes, ' Trans. Geol. Soc.,' ser. 2, vol. vii (1846), p. 156, pi. xviii, fig. 6. O. ponticeriana, d'Orbigny, 

 * Voy. Pol. Sud etl'Oceanie. Atlas Geol.' (1847), pi. viii, figs. 45, 46. ? O. larva ?, Kner, ' Kreidemerg. 

 v. Lemberg' (1850), p. 30, pi. v, fig. 4. O. u roga Hi, Quenstedt, ' Handb. d. Petref actenkunde ' (1852), 

 p. 499, pi. xl, fig. 24. O. larva, Beyrich, ' Zeitscbr. deutsch. geol. Gesellsch.,' vol. iv (1852), p. 153, 

 pi. iv, fig. 3. ? O.frons, Kner, ' Denkschr. Akad. Wiss. Wieu, Math.-nat, CI.,' vol. iii (1852), p. 319, 

 pi. xvii, fig. 10. ? O. larva, Favre, ' Moll. Foss. de la Craie de Lemberg' (1869), p. 160. O. ungulata, 

 Coquand, ' Mou. Ostrea, Terr. Cret.' (1869), p. 58 (partim), pi. xxxi, figs. 4, 5, 12—15. O. (Alec- 

 tryonia) ungulata, Stoliczka, ' Cret. Fauna S. India,' vol. iii (1871), p. 470, pi. xlvii, figs. 3, 4. O. larva, 

 Lartet, 'Ann. Sci. gcol.,' vol. iii (1873), p. 59. Alectryonia larva, Schroder, 'Zeitscbr. d. deutsch. 

 geol. Gesellsch.,' vol. xxxiv (1882), p. 262. O. (Alectryonia) larva, White, ' Ostreidae of N. America' 

 (1884), p. 296, pi. xlii, figs. 7 — 9. 0. ungulata, Peron, 'Hist. Terr, de Craie S.E. Bassin Anglo- 

 Parisien' (1888), p. 178. O. (Alectryonia) larva, Griepenkerl, ' Senon. v. Koiiigslutter ' (' Palaeont. 

 Abhandl.,' vol. iv, 1889), p. 33. O. ungulata, Holzapfel, ' Mollusk. Aachen. Kreide ' ('Palseonto- 

 graphica,' vol. xxxv, 1889), p. 250. Alectryonia ungulata, Newton, ' Quart. Journ. Geol. Soc.,' vol. 

 xlv (1889), p. 333, pi. xiv, fig. 12. O. ungulata, Peron, 'Descript. Brach., etc., Terr. Cret. Tunisie ' 

 (1890 — 91), p. 185. O. ungulata, Bohin, ' Palaeontographica,' vol. xxxviii (1891), p. 91. A. ungulata, 

 Newton, 'Journ. Conch.,' vol. viii (1896), p. 136. O. (Alectryonia) ungulata, Notling, ' U. Cret. 

 (Maestrichtian) Mari Hills ' ('Palseont. Indica,' ser. xvi, vol. i, 1897), p. 38, pi ix, figs. 4, 5. ? O. cf. 

 larva, Quaas, ' Palaeontographica,' vol. xxx, 2 (1902), p. 187, pi. xxi, fig. 12. O. (Alectryonia) ungulata, 

 Boule and Thevenin, 'Annal. Palcont.,' vol. i (1906), p. 48 [6], pi. i, fig. 5. A. larva, Krumbeck, 

 ' Palaeontographica,' vol. liii (1906), p. 96, pi. vii, fig. 10. O. (Alectryonia) ungulata, Petho, ibid., 

 vol. Iii (1906), p. 185, pi. xii, fig. 1. 



