100 CRETACEOUS LAMELLIBRAXCHIA. 



1846. Pinna decussata, A. E. Reuss. Die Versteiu. dor bohui. Kreidcforuiat., 



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

 1850. — — A. (VOrhigny. Prodr. tie Pal, vol. ii, p. 165. 



— — FENESTEATA, (V Ofbiytiij. Ibid., p. 246. 



— — DECUSSATA, J. de C. Sowerhy, in F. Diron. Geol. Sussex, p. 355 (p. 



386, ed. 2), pi. xxviii. 

 fig. 20. 



— — DiLuviANA, H. B. Geinitz. Das Quadersandst. oder Kreidegeb. iu 



Deutsclilaud, p. 166. 



— — FENESTKATA, Gciiiitz. Ibid., p. 166. 



1854. — DECUSSATA, /. Morfis. Cat. Brit. Foss., ed. 2, p. 180. 



— — SULCATA, Morris. Ibid., p. 180. 



1873. — DECUSSATA, H. B. Geinitz. Das Elbthalgeb. in Sachseu (Palipouto- 



grapliica, 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, ini Gebiete der bolim. Kreideforiiiat., 



ii. Weisseuburg. u. Maluitz. Scliicht., p. 

 120, fig. 86. 

 1883. — — Fritsch. Ibid., iii. Iserscbicht., p. 104. 



1888. — — G. Mailer. MoUusk. d. uutersen. v. Biauuscliwoig (Jalirb. 



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

 p. 420. 



1889. — — Fritsch. Stud, im Gebiete dor bohm. Kreidoformat., 



iv. Teplitz. Scbicht., p. 79. 

 ? 1890. — — M. Blanchenhorn. Beitr. z. Geol. Syi'iens : Kreidesjst. 



in Mittel u. Nord-Svrion. p. 80. 

 1893. — — Fritsch. Stud, ini Gebiete der biihm. Kreideforinat., 



V. Priesen. Scliicht., p. 94. 

 1897. — -_ _ Ibid., vi. Chloinok. Sdiicht., p. 57. 



? 1894. — cf. DECUSSATA, A. Henniij. Oui Ahussandst. (Geol. Foreu. i Stook- 



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

 1902. — DECUSSATA, J. P. J. Eavn. Mollusk. i Danmarks Kridtaflej., i. 



Lainellibr., p. 104. 



Non 1846. — — E. Forbes. Trans. Geol. Soc, ser. 2, vol. vii, p. 1.53 



(= 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 l)y 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 ril)s and interspiices at regular intervals. The dorsal portion of 



