MODIOLA. 95 



? 1873. MoDioLA REVEESA, var., H. B. Gehiitz. Das Elbthalgeb. iu Saclisen 



(Palseontograpliica, vol. xx), pt. 1, p. 216, 

 pi. xlviii, fig. 9. 



Non 1844. Mttilus keveesus, A. d'Orhigiiy. Pal. Fran9. Terr. Cret., vol. iii, p. 264, 



pi. cccxxxvii, figs. 1, 2, 

 ? 1846. MoDioLA EEVEESA, A. E. Beuss. Die Versteiu. der bolirn. Kreideformat., 



pt. 2, p. 15, pi. xxxiii, 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 lines are seen on other parts of the shell. 



Measurements : 



(1) (2) 

 Length 71 70 



Greatest diameter perpendicular 



to length . . . 29 30 



Thickness .... 27 — 



(1 — 6) all from Blackdown. 



Affinities. — The form figured by d'Orbigny as M. reversus (Sowerby), but after- 

 wards separated as M. Fittoni, d'Orbigny,^ appears to differ from Sowerby's species 

 in the possession of a distinct carina, and in having the umbones placed less 

 anteriorly. 



M. fypica (Forbes),^ especially as represented by the forms from Gosau, is 

 closely allied to M. reversa. 



M. albensis (d'Orbigny)"' 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 BlackdoAvn. 



1 For the syuouymy of this species see Pictet aud Campiche, ' Foss. Terr. Crt't. Ste. Croix ' 

 (Mater. Pal. Suisse, ser. 4, 1867), p. 495. 



2 ' Trans. Geol. Soc.,' ser. 2, vol. vii (1846), p. 152, pi. xiv, fig. 4 ; Zittel, " Die Bivalv. der Gosaugeb." 

 (' Denkschr. d. k. Akad. Wisseusch. Math.-nat. Classe,' vol. xxv, 1866), pt. 2, p. 78 (p. 2 of reprint), 

 pi. xi, fig. 5; Stoliczka. 'Cret. Fauna S. India,' vol. iii (1871), p. 377, pi. xxiii, figs. 12—15. 



■' Pictet and Campiche, op. cit., p. 504, pi. cxxxiv, fig. 1. 



(3) 



(4) 



(5) 



(6) 



58 



54 



34 



21 mm, 



26 



22 



15 



12 



22 



21 





^^ 



