100 CRETACEOUS LAMELLIBRANCHIA. 



18-46. Pinna decussata, A. E. Beuss. Die Verstein. der bohm. Kreideformat., 



pt. 2, p. 14, pi. xxxvii, figs. 1, 2. 

 1850. — A. d'OrUgny. Prodr. de Pal., vol. ii, p. 165. 



— fenestrata, d'Orbigny. Ibid., p. 246. 



— decussata, J. de C. Sowerby, in F. Dixon. G-eol. Sussex, p. 355 (p. 



386, ed. 2), pi. xxviii, 

 fig. 20. 



— — diluviana, H. B. Geinitz. Das Quadersandst. oder Kreidegeb. in 



Deutscliland, p. 166. 



— — fenesteata, Geinitz. Ibid., p. 166. 



1854. — decussata, /. Morris. Cat. Brit. Foss., ed. 2, p. 180. 



— — sulcata, Morris. Ibid., p. 180. 



1873. — decussata, H. B. Geinitz. Das Elbthalgeb. in Sachsen (Palaxmto- 



graplvica, vol. xx), pt. i, p. 211, pi. xlvii, 

 figs. 4, 5 ; pt. ii, p. 53, pi. xv, figs. 2, 3 ; 

 pi. xvi, fig. 1. 

 1877. — A. Fritsch. Stud, im Gebiete dei bohm. Kreideformat., 



ii. Weissenberg. u. Malnitz. Schiclit., p. 

 120, fig. 86. 

 1883. — Fritsch. Ibid., lii. Iserschicht., p. 104. 



1888. — G. Midler. Mollusk. d. untersen. v. Braunschweig (Jahrb. 



d. k. preussisch. geol. Landesanst. fur 1887), 

 p. 420. 



1889. — — Fritsch. Stud, im Gebiete der b6hm. Kreideformat., 



iv. Teplitz. Schiclit., p. 79. 

 ? 1890. — — M. Blanckenhorn, Beitr. z. Geol. Syriens : Kreidesyst. 



in Mittel u. Nord-Syrien, p. 80. 

 1893. — — Fritsch. Stud, im Gebiete der bohm. Kreideformat., 



v. Priesen. Schiclit., p. 94. 

 1897. — — — Ibid., vi. Chlomek. Schiclit,, p. 57. 



? 1894. — cf. decussata, A. Hennuj. Om Ahussandst. (Geol. F6ren. i Stock- 

 holm Forhandl., vol. xvi), p. 522. 

 1902. — decussata, J. P. J. Bavii. Mollusk. i Daniuarks Kridtaflej., i. 



Lamellibr., p. 104. 



Non 1846. — E. Forbes. Trans. Geol. Soc, ser. 2, vol. vii, p. 153 



(= P. arata, Forbes). 



Description. — Shell moderately elongate, triangular, laterally compressed, 

 section rhombic, but becoming lenticular in the later portion. Dorsal margin 

 straight, ventral margin slightly curved. 



Each valve is divided into two nearly equal parts. The dorsal part is flattened 

 and bears from 7 to 9 strong rounded ribs, separated by broad, shallow, 

 rounded depressions. The distance between the ribs increases in passing from the 

 apex to the posterior extremity. In well-preserved specimens linear ridges are 

 seen crossing the ribs and interspaces at regular intervals. The dorsal portion of 



