MYOCONCHA. 115 



1844. Mtoconcha cretacea, A. d'Orbigny. Pal. Frau9. TeiT. Cret , vol. Hi, 



p. 260, pi. cccxxxv. 

 ? 1847. — — A. cVArchiac. Mem. Soc. gt'ol. France, ser. 2, 



vol. ii, p. 307. 

 1850. — _ ^. d'OrLhjmj. Proclr. de Pal., vol. ii, p. 165. 



1854. — —J. Morris. Cat. Brit. Foss., ed. 2, p. 214. 



1862. — — J. G. Cheim. Manuel de Conch., vol. ii, p. 155, 



fig. 766. 

 1866. — — F. J. Ptdet and G. Cainpiche. Moll. Foss. Terr. 



Cret. Ste. Croix (Mater. Pal. Suisse, ser. 4;. 

 p. 344. 

 ? 1868. — — E. Eichwald. Lethaea Rossica, vol. ii, p. 588, 



pi. xxii, fig. 10. 



Vescri^ption. — Shell suljtriangular, or more or less oblong, gradually increasing- 

 in height posteriorly. Anterior end blunt, rounded; posterior border rounded, 

 somewhat oblique ; ventral border nearly straight. Valves flattened, gradually 

 compressed posteriorly, more sharply compressed towards the ventral margin. 



Ornamentation consists of slender, equidistant, slightly curving, radial ribs, 

 which are absent near the dorsal margin ; the most dorsal rib is stronger than the 

 others. The radial ribs are crossed regularly by numerous slender concentric ribs 

 which are parallel to the growth-lines. 



Mensuremeiifs : 



Length ......... 74 nun. 



Height 88 „ 



Thickness . . . . . . . . . 28 „ 



Affinities. — 1/. lietjuieniana , Matheron,' is less expanded posteriorly, and more 

 concave ventrally. 



Mi/oconcha, n. sp., Miiller," may be an allied form, but is known only by internal 

 moulds. 



Types. — From the Cenomanian of Saintes, Angouleme, Rouen, etc. 



Distribution. — Basement bed of Chalk Marl (zone of Schloenbachia varians) of 

 Chard, Maiden Xewton, and Evershot. Chloritic Marl of Maiden Bradley, "Wool- 

 combe, and Toller Fratrum.^ 



• 'Cat. Foss. Bouclies-dii-Eli6ne' (1842), p. 177, pi. xxviii, figs. 3, 4. D'Orbigny, ' Prodr. de 

 Pal.,' vol. ii (1850), p. 196. 



- "Die Mollusk. d. Unterseu. v. Braunschweig u. Ilsede " ('Abliandl. d. k. preuss. geol. Land.,' 

 n. F., pt. 25, 1898), p. 48, pi. vii, fig. 3. 



' Casts of Myoconcha, from the Lower Greensand of Seend, are preserved in the Museum of 

 Pi-actical Geology, but the species cannot, at present, be determined. 



