MODIOLA. 95 
?1873. Moproua reversA, var., H. B. Geinitz. Das Elbthalgeb. in Sachsen 
(Paleontographica, vol. xx), pt. 1, p. 216, 
pl. xlviii, fig. 9. 
Non 1844. Myrinus reversus, A. d’Orbigny. Pal. Franc. Terr. Cret., vol. iii, p. 264, 
pl. ccexxxvil, figs. 1, 2. 
21846. MoproLa reversa, A. FE. Reuss. Die Verstein. der bohm. Kreideformat., 
pt. 2, p. 15, pl. xxxii, fig. 9. 
Description.—Shell elongate-oval, extremities rounded; median part of shell— 
from the umbo to the posterior extremity—inflated and slightly curved; dorsal 
part compressed and somewhat extended. Ventral to the inflated part is a shallow 
depression. Hinge margin forms an obtuse angle with the oblique and slightly 
convex posterior margin. Ventral border sinuous. Umbones obtuse; no carina. 
Ornamentation consists of concentric ridges, often sharply marked, sometimes dis- 
continuous and rather irregular; between these are seen, in some specimens, much 
finer ridges. A bundle of fine radial ribs extends from the umbo to the ventral 
sinuosity and occupies the greater part of the shallow depression ; occasionally fine 
close-set radial Imes are seen on other parts of the shell. 
Measurements : 
@) (2) (3) ©) ) (6) 
Length . ; : ; . 71 70 58 54 34 21 mm. 
Greatest diameter perpendicular 
to length ; 5 x 29» “30 (26% 2oee ope si omeee 
Thickness. ; 27 — 22 21 — — 
(1—6) all from Blackdown. 
Affinities—The form figured by d’Orbigny as M. reversus (Sowerby), but after- 
wards separated as M. Fiitoni, VOrbigny,' appears to differ from Sowerby’s species 
in the possession of a distinct carina, and in having the umbones placed less 
anteriorly. 
M. typica (Forbes),’ especially as represented by the forms from Gosau, is 
closely allied to M. reversua. 
M. albensis (VOrbigny)’ is very near to M. reversa, but is perhaps distinguished 
by the somewhat longer and less curved anterior margin. 
For the relation of this form to M. ligeriensis (d’Orbigny) see below. 
Type.—In the Bristol Museum, from Blackdown. 
1 For the synonymy of this species see Pictet and Campiche, ‘ Foss. Terr. Crét. Ste. Croix’ 
(Matér. Pal. Suisse, ser. 4, 1867), p. 495. 
* «Trans. Geol. Soc.,’ ser. 2, vol. vii (1846), p. 152, pl. xiv, fig. 4; Zittel, “ Die Bivaly. der Gosaugeb.” 
(‘Denkschr. d. k. Akad. Wissensch. Math.-nat. Classe,’ vol. xxv, 1866), pt. 2, p. 78 (p. 2 of reprint), 
pl. x1, fig. 5; Stoliczka, ‘Cret. Fauna 8. India,’ vol. iii (1871), p. 377, pl. xxiii, figs. 12—15. 
5 Pictet and Campiche, op. cit., p. 504, pl. exxxiy, fig. 1. 
