BIVALVIA. 61 



umbones are larger ; the concentric nigaj will also at once distinguish it, as the young shell 

 of S. Madridi is smooth. 



GeoIo(/icul Fosi/io?i.s and LocaHlies. The Great Oolite of Hampton cliifs ; the Corn- 

 brash of Lajcock. In the collection of W. AValton, Esq. 



Opis Leckenbyi, IFri^ht. Tab. XXXVII, figs. 9, 9 ^. 



Opis Leckenbyi, Wright, iu Proc. Geol. Soc, vol. xvi, part 1, 18G0. 



Testa crassa, trigona, ohliqua^ fornicata, inaquilatera, cordiformi, transverse regidariter 

 cosfafa, postice acute carinata, umhonibus magnis elevafis, anticis, involutis, latere antico 

 6revissifno, postico suhrecto oblique declivi ; lunula magna profunda, marghiibus obtusis, 

 striatis ; costis transversis, regularibus, angusiis, subacutis ; valvis striis longitudinalibus el 

 decussantibu!^ subtillissimis insfructis. 



Shell thick, trigonal, oblique, very convex, and insequilateral, cordiform, vi'ith transverse, 

 regular costse ; a large, flattened, posterior area is separated from the other portion of the 

 shell by an elevated, acute carina, anterior and parallel to which is a slight depression ; the 

 umbones are large, elevated, much inclined forwards, and involute ; the anterior side is 

 very short, having a large and deep lunule, whose margin is rounded and striated ; the 

 costa? upon the sides of the valves are regular, narrow, subacute, and not much elevated ; 

 the wide, posterior area has large, oblique striations ; the costated portion is covered with 

 extremely fine perpendicular and decussating striations, whicli are only distinguishable 

 under a magnifier. 



Height, 15 lines; length, 15 lines ; diameter through both the valves, 13 lines. 



A large and elegant species, distinguished from Opis lunulatus. Sow., by the more con- 

 vex figure, the rounded margins of the lunule, and by the more acute and more densely 

 arranged costse ; the posterior carina and bordering sulcation are also very prominent 

 features ; the costse under a magnifier exhibit a beautifully decussated surface. 



Geological Position and Localitg. The Cornbrash of Scarborough ; a single specimen 

 in the collection of Mr. Leckenby. 



Opis pulchella, D'Orb. Part II, Tab. VI, fig. 3, p. SO. 



Opis pulchella, jyOrhujmj. Prodrome, i, p. 307. 

 — LUNULATUS, var. Great Ool. Mod., Pal. Soc, part 2, pi. 6, fig. 6, p. SO. 



Espece voisine de V 0. lunulata, mais bien plus courte et moins oblique, presque carree 

 ornee de cotes concentriques." (D'Orbigny.) 



The experience derived from a multitude of examples leaves no room to doubt that the 



