OSTREA. 347 



1908. OsTREA (Alectryonia) maceoptera, p. a. Peron. Compte rendu Assoc. 



Franf. Avanc. Sci., 

 vol. xxxvi (1907), 

 p. 308. 



1910. — — CARINATA, E. Buse. Mon. geol. paleont. Cerro 



de Muleros (Bol. Instit. 

 geol. Mexico, No. 25), p. 

 104, pi. xvi, figs. 13, 14. 



1911. — (Alectronia) cxRiNATA, a. Fritsch. Stud, im Geldete der bohm. 



Kreideformat., Korycaner 

 Schiclit., p. 48, fig. 218. 



— — DiLUViANA, Fritsch. Ibid., p. 48, fig. 216. 



— Alectryonia diluviana, K. Vogel v. Falclcenstein. Zeitsclir. d. deutsch. 



geol. Gesellsch., vol. Ixii, p. 659. 

 ? — — cfr. FRONS, Vogel v. Falckenstein. Ibid., p. 559. 



Nou 1847. OsTREA CARINATA, J. MHUer. Petref. der Aachen. Kreidef., pt. ], p. 38, 



(=0. Goldfussi, Holzapfel). 



— 1850. — — /. de C. Sowerhi/, in F. Dixon. Geol. Sussex, p. 357 {0. 



frons, p. 386, ed. 2), 

 pi. xxvii, fig. 2. 



— 1852. — FROas ? B. Ener. Denksclir. k. Akad. Wissenscli. Wien, Math. -Nat. 



CL, vol. iii, p. 319, pi. xvii, fig. 10. 



— 1883. — — A. Fritsch. Stud, im Gebiete der bohui. Kreideformat., 



iii, Iserschicht., p. 121, fig. 96. 



Description. — Sliell nearly equivalve ; the valves similar except for the attached 

 surface of the left valve. The proportion of height to length varies, but usually 

 the height is much greater than the length, the difference becoming greater with 

 age. Valves usually more or less tapering towards the postero-ventral extremity, 

 but occasionally expanding at the end ; slightly, moderately, or considerably 

 curved, occasionally forming a nearly complete volution ; sides flattened, so that 

 in the elongate forms each valve is roof-like in section. The thickness (or depth) 

 of the valves increases with age, and in old individuals the shell becomes very 

 thick and possesses a vesicular structure. Umbones siniill, with a slight or 

 moderate posterior curvature. A posterior wing or ear is usually present, and is 

 of small or moderate size when the attached surface is small, but of large size 

 when the attached surface is large and mainly posterior to the umbo. A small 

 anterior wing is often present, and is best developed in specimens which have a 

 small attached surface. When the attached surface is small or narrow the shell 

 becomes elongate, but when the attached surface is large and broad the shell 

 becomes rounded or oval instead of elongate, and then the posterior ear is usually 

 not distinctly defined. 



