72 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



shorter, more convex, the test thicker, the umbones larger, less oblique, and more obtuse ; 

 the posterior flattened area is also a distinguishing feature when it is present. 



Geological Position and Localities. The Forest Marble of Laycock and Parleigh, in 

 the collection of W. Walton, Esq., of Bath. 



ASTABTE UNGULATA, 'PhU., sp. Tab. XXXV, fig. 20. 



AsTAKTE LURiDA, FJiil. Geol. York., i, pi. 5, fig. 2, p. 137, non A. lurida, Sow. 



— — Williamson. Trans. Geol. Soc, 2d ser., vol. vi, p. 149. 



— — Bean, on Cornbrash Fossils, Mag. Nat. Hist., 1839. 



— — Leckenby, on Kelloway Rock Fossils, Journ. Geol. Soc, 1858. 



I'esta suborbiculari aut subquadranc/ulari, depressa^ incequilatera, ad periphcBriam con- 

 centrice costellata^ costellis elevatis, subangularibiis, concentrice subtillissime striatis ; 

 cosfellis in/erne evanescentibus ; margine cardinali curvato, lunula subnulla. 



Shell suborbicular or somewhat subquadrangular, depressed, inequilateral ; umbones 

 small and only slightly produced ; posterior and inferior margins rounded, lunule, 

 obsolete ; the surface near to the umbo with elevated acute concentric rugae, which are 

 impressed with very delicate concentric striations ; the rugae disappear towards the middle 

 of the valve, the lower portion having only some plications of growth. 



The character of the surface has a considerable resemblance to Astarte Wiltoni, ' Gr. 

 Ool. Monogr.,' Tab. IX, f. 16 ; but the latter has the umbo much more produced, it has a 

 distinctly excavated lunule and is more convex ; other depressed species are sufficiently 

 separated by their ornamentation. 



Astarte lurida. Sow., which occurs in Gloucestershire at Nailsworth in gray shale 

 near to the upper boundary of the Upper Lias, and in the lower portion of the overlying 

 Supraliassic Sands associated with Ammonites variabilis, is a very different shell, whose 

 figure is ovately trigonal and moderately convex, with prominent apex, well-marked lunule 

 and depressed concentric rugae ; it does not therefore present a near approximation to our 

 species. 



Astarte nngulata has the height and lateral diameter equal ; the valves are moderately 

 thick ; the size varies from 4 to 10 lines across. It is rare. 



Geological Positions and Localities. Professor Phillips figured the interior of a valve 

 from the Oxford Clay of Scarborough. Mr. Leckenby has recorded it in the Kelloway 

 Rock of the same locality ; our figure is taken from a Cornbrash specimen of the same 

 coast now in the collection of Mr. Leckenby, and formerly in that of Mr. Bean, who 

 identified the species with that originally figured in the ' Geology of Yorkshire.' 



