BIVALVIA. 79 



ASTARTE FLEXICOSTATA, Li/c. Tab. XL, fig. 2G. 



Testa transKersa^ suhlri/j/ona, convexa, umbonibus anticis acuHs, elevati^, mnrgine an- 

 teriore truncata, abrupfe declivi in/erne angula formante ; lunula magna lavigata concava, 

 margine acuto ; margine inferiore subrecto ; marginc posteriore imprimis subhorizonfali 

 j)ostice oblique declivi ; superjicie striis concentricis regularibus instructis, in medio evanes- 

 cent ibus. 



Shell transverse, subtrigonal, convex ; umbones anterior, pointed, and conspicuous ; 

 anterior side truncated, descending abruptly, and forming an angle with the lower border 

 at its extremity ; the lunule is large, concave, smooth, with an acute margin ; the lower 

 border is nearly straight ; the posterior margin is nearly horizontal for the half of its length, 

 then slopes obliquely downwards ; the shell is moderately convex, with an oblique, obtuse 

 angle, posterior to which the surface is more flattened ; it has regular striations, \vhich 

 follow the direction of the lines of growth ; they are conspicuous near to the umbones, 

 but disappear upon the middle portion of the dorsal surface. 



Height, 5 lines ; length, 7 lines ; diameter through the united valves, 3| lines. 



Geological Position and Locality. Collected by E. Witchell, Esq., in the white stone 

 (Great Oolite) of Bussage, near to Bisley Common ; a single specimen. 



Gresslya peregrin a, PJdl., sp. Tab. XXXVI, figs. 2, 2 a, b. 



In addition to the specimen figured in PI. XV, Part II of the ' Great Oolite Monograph,' 

 it has been deemed advisable to exemplify three other variations of form, by the aid of 

 which the intermediate connecting links may readily be imagined. This Gresslya is very 

 abundant in the Cornbrash, both in Wiltshire and Yorkshire, so that ample opportunities 

 are afforded of studying every variation of form which it presents ; these, as will be seen 

 from our figures, are so considerable and so common that it seems impossible fairly to 

 disconnect from them some other examples of Gresslya from the Inferior Oolite, as Unio 

 abductvs, Phil., Gresslya latior, Ag., G. conformis, kg., G. lunulata, Ag., G. erycina, Ag., 

 G. concentrica, Ag., and perhaps also G. zonata, Ag. In all these the same kind of 

 surface obtains, and the outer, granulated tegument is precisely identical, belonging to 

 that section of the genus in which the radiating lines and the granules are of the most 

 minute size, and very densely arranged. It has been usual to select for G. abducta 

 Inferior Oolite examples with short forms, elevated umbones, tumid anterior sides, and 

 compressed posterior sides ; but the shortness of figure is surpassed by some from the 

 Cornbrash, and the inflation of the anterior side varies in amount with every specimen. 

 From these, probably, must be separated G. latirostris, Ag., which attains to large 



