BIVALVIA. S5 



Localities. The vertical range of this remarkable species is very considerable ; it occurs 

 in the Inferior Oolite of the Cotteswolds, the Great Oolite of Minchinhampton, the 

 Coralline Oolite of Malton, and we have seen fine casts from the Kimmeridge Clay of 

 Wilts. The Hippopodium Luciense and 77. Bajociense, D'Orb., are probably identical with 

 this species. 



ASTARTE EXCAVATA, Sow., Var. COMPRESSIUSCULA. Tab. IX, fig. IS, 19. 



Astaete excavata, Sow. MiD. Con., t. 233. 



— complanata, Roemer. Nordd. Oolith., t. 6, f. 28. 



Testa ovatd, transversa, compressd, umbonibus parvis anticis depressis, margine cardinal), 

 elongato, carvato, subliorizontali, margine inferiore ettiptico, lunula angustd excavatd, 

 margine acuto. Costis externis concentricis depressis irregularibus interdum confertis ant 

 enim obsoletis. JEtate juniori testa planatd etfragili, costis paucis laf is prominulis. 



Shell ovately transverse, compressed ; umbones small, anterior, and much depressed ; 

 hinge border elongated, nearly horizontal, and curved ; lower border regular, elliptical ; 

 lunule deeply excavated, its margins acute ; concentric cost* depressed, irregular, some- 

 times nearly obsolete. In the young state the shell is flattened, very delicate, pellucid, and 

 has a few distinct broad concentric costae near to the umbones. 



In the shelly beds of the Great Oolite, the young delicate shells occur abundantly from 

 3 to 6 lines in length. Adult specimens are much more rare, and few exceed 20 lines in 

 length. 



The tenuity of the test is considerable ; and this feature, together with the greater 

 flatness, will serve to distinguish it from the typical form, A. excavata, Sow., which is a 

 much larger and thicker shell. Notwithstanding its tenuity, flatness, and the small 

 dimensions, we believe this to be only a variety of the well-known Inferior Oolite shell, 

 induced by peculiarities of the stratum in which it occurs. The same change of aspect takes 

 place in the freestone beds of the Inferior Oolite ; but the form again attains its pristine 

 dimensions and thickness in the upper ragstones higher in the series. 



Localities. Minchinhampton Common in the Great Oolite ; Nailsworth Hill, in the 

 freestone beds of the Inferior Oolite. 



The typical shell occurs abundantly at Dundry and at Rodborough Hill. 



Astarte depress a, Gold/. Tab. IX, fig. 11. 



Astaete depeessa, Goldfuss. Petref., p. 192, t. 131, f. 11. 



Testa compressd, transversim ovato-orbiculari ; umbonibus mediants obtusis ; lunula 

 ellipticd, angustd, costis convexis in tersf Usque concentrice striatis. (Goldfuss.) 



Shell compressed, transverse, ovately orbicular ; umbones median, prominent, obtuse ; 



