20 CRETACEOUS LAMELLIBRANCHIA. 



Non 1847. A.d'Orligny. Pal. Fran?. Terr. Cre't., vol. iii, p. 564, pi. 



ccccxxiv, figs. 1013. 



1847. MANTELLI, d'Orbigny. Ibid., p. 568, pi. ccccxxvi, figs. 35. 



1850. HOPERI, d'OrUgny. Prodr. de Pal., vol. ii, p. 248. 



MANTELLI, d'Orbigny. Ibid., p. 248. 



1877. HOPERI, A. Fritsch. Stud, im G-ebiete der bohm. Kreideformat. : 



II, Weissenberg. u. Malnitz. Schicht., p. 134, 

 fig. 121. 



MANTELLI, Fritsch. Ibid., p. 134, fig. 122. 



1872. HOPERI, H. B. Geinitz. Das Elbthalgeb. in Sachsen (Palseonto- 



graphica, vol. xx, pt. 2), p. 40, pi. ix, 

 figs. 11, 12. 



1881. J. Kiesow. Cenomanverstein. a. d. Diluvium d. Umgeg. 



Danzig's (Schrift d. naturf. Gesellsch. in 

 Danzig, N. F., vol. v), p. 414, figs. 9, 10. 



? 1893. sp., cf. HOPERI, E. Michael. Zeitschr. d. deutsch. geol. Gesellsch., 



vol. xlv, p. 234. 



Description. Shell convex, oval, rounded, considerably inequilateral, longer 

 than high. Antero-dorsal margin rather long, slightly convex or nearly straight ; 

 postero-dorsal margin rather short ; the remainder forming a regular curve. 

 Umbones close together. Apical angle 115 to 117. Ears rather small, with 

 growth-lines; the posterior longer than high and larger than the anterior ear. 

 Anterior area large, deep, with a more or less sharp border, often with radial 

 grooves which vary in number and are more distinct near the umbo than 

 anteriorly. 



Surface of shell nearly smooth. In the region of the umbo numerous linear 

 grooves with pits occur ; these may also extend on to the anterior and posterior 

 parts of the shell, and in some cases they are present on the middle of shell, 

 reaching a part of the way or even quite to the ventral margin. The grooves are 

 slightly wavy, sometimes discontinuous, and are deeper near the anterior and 

 posterior margins, and often more widely separated near the former. New 

 grooves are introduced at various distances from the umbo. 



Measurements : 



(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 



Length 57 57 56 52 51 51 47 41 37 34 31 31 mm. 

 Height 52 50 52 50 47 46 42 39 32 32 28 26 

 (1) M. cor-anguinum zone, G-ravesend. (5, 10) M. cor-anguinum zone, Northfleet. 



(2) Uintacrinus band, Devizes Eoad, 



Salisbury. 



(3, 6, 12) A. quadratus zone, East Harnham. 

 (4, 7) M. cor-anguinum zone, Gravesend. 



(8) Chalk Kock, Underwood Hall, Dulling- 



ham. 

 (9, 11) B. mucronata zone, Norwich. 



Affinities. This species was described by Brongniart under the name Plagios- 

 toma Mantdli from specimens which were sent to him by Mantell from near 



