MODIOLA. 93 
1858. Mytrnus mauauis, F. J. Pictet and E. Renevier. Foss. Terr. Aptien 
(Matér. Pal. Suisse, ser. 1), p. 116, pl. xvi. fig. 2. 
1865. — —  H. Coquand. Mon. Aptien de l’Espagne, p. 143. 
1868. — — BE. Bichwald.  Lethzea Rossica vol. ii, p. 531. 
1867. -= -- FP. J. Pictet and G. Campiche. Foss. Terr. Crét. Ste. 
Croix (Matér. Pal. Suisse, ser. 4), pp. 496, 507. 
1883. Moprona oprsa, W. Keeping. Foss., &c., Neoc. Upware and Brickhill, 
p. 117, pl. vi, fig. 3. 
y Non 1846, — #quaris, A. B. Reuss. Die Verstein. der bihm. Kreideformat., 
pt. 2, p. 15, pl. xxxiii, fig. 10. 
— 1866, —— —_ K. A. Zittel. Die Bivalv. der Gosaugeb , pt. 2 
(Denkschr. d.k. Akad. Wissen. Math.-nat. Cl. Wien, 
vol. xxv), p. 80 (p. 4 of reprint), pl. xi, fig. 4. 
— 1882. — — J. Kiesow. Schrift. der nat. Gesell. in Danzig, vol. vy, 
p. 240. 
P— 1885. — - F. Nétling. Die Fauna der baltisch. Cenom. (Palewont. 
Abhandl., vol. ii), p. 24, pl. iv, fig. 1. 
Description.—Shell ovate-oblong, rather short, rounded at the ends, convex, 
compressed posteriorly. Dorsal and ventral margins usually nearly parallel. 
Umbones obtuse, not terminal. Carina absent or very indistinct; greatest con- 
vexity of valve between the umbo and the postero-ventral extremity. <A. slight 
mesial groove produces a small sinus near the middle of the ventral margin. 
Surface smooth except for the presence of small concentric ridges, which are best 
marked anteriorly and postero-dorsally. 
Measurements : 
a @ @ @ © £6) (7) 
Leneth : > 20 28 27 22:5. 22 2] 15 mm. 
Height . : s Paes: Loi 12 2 oles Ot oa, 
Thickness. oe ees 15 14 Lhe 10 9257 eT 
(1—7) all from the Crackers of Atherfield. 
Affinities —The young forms of M. reversa, Sowerby, are distinguished from 
this species by the greater obliquity of their ventral margins. M. Fitton’, dOrbigny,' 
appears to differ from M. xqualis in the presence of a distinct carina with radial 
striz in front of it, and also in its greater length. 
Forbes and Morris considered that M. Archiaci, Leymerie,? and M. bipartita, 
Leymerie, on Sowerby, were identical with MM. equalis. Some of our specimens 
agree very closely with Leymerie’s figures of the latter, but with the former the 
agreement is not quite so satisfactory; the figures given by d’Orbigny,® and by 
1 «Prodr. de Pal.,’ vol. 11 (1850), p. 81. 
* *Mém. Soe. géol. France,’ vol. v (1842), p. 8, pl. x, fig. 2. 
3 «Pal. Franc. Terr. Crét.,’ vol. iii (1845), p. 291, pl. ecexliv, figs. 1O—12. 
