162 Mr. J. Lycett on the Upper Lias of Gloucestershire. 



Placunopsis sparsicostatus, n. sp. 



Shell flattened, suborbicular, oblique ; umbo raised, submar- 

 ginal, the surface with numerous irregular, unequal, concentric 

 plications, and a few raised, equal, linear, distant, undulating 

 and radiating ribs, sometimes slightly knotted where they pass 

 over the plications. Diameter 12 lines. A single good specimen. 



Nucula Hausmanni, Roem. Nearly allied to Nucula Erato, 

 D'Orbigny, an Inferior Oolite shell both of Yorkshire and 

 Gloucestershire; but the latter species is less angular, less pointed 

 at the extremities, or more ovate and smaller. A single fine 

 specimen. 



Posidonia Bronnii, Miinst. A delicate papyraceous and some- 

 what irregular shell, usually indifferently preserved, but occurring 

 throughout a thickness of about two inches in tender, thinly 

 laminated shale. Impressions are abundant, but the test is 

 rarely preserved. 



Astarte lurida, Sow. So numerous are the Jurassic species 

 of Astarte, and in many instances so nearly allied are they to 

 each other, that the utmost care and precision is necessary, both 

 in descriptions and figures, to convey clear and correct ideas of 

 them in the absence of the fossils ; nor under any circumstances 

 can the varieties of aspect which they assume, and the bounda- 

 ries between species, be in every instance sufficiently defined. 

 The figure of Astarte lurida in the ( Min. Conch/ accurately re- 

 presents a short specimen in the young state, before the arrests of 

 growth had produced irregularity and inequality in the encircling 

 ribs, the verbal description appended being very concise. The 

 following description is the result of an examination of a multi- 

 tude of specimens in every stage of growth : 



Shell oblique, ovate, moderately convex; umbones anterior, 

 pointed, and incurved ; anterior side very short ; lunule large, 

 striated, elliptical, excavated, its margin slightly rounded ; liga- 

 mental margin lengthened, its outline somewhat curved, forming 

 with the other valve a lengthened, smooth, but not deeply exca- 

 vated area with acute borders ; lower margin elliptically curved, 

 internally crenulated. Surface with elliptical costse, regular in 

 the young shell, subsequently degenerating into irregular and 

 unequal elevations, more especially when the surface exhibits 

 arrests of growth ; the costae are not much raised, rounded, and 

 fully equal in breadth to the interstitial spaces (about thirty-two 

 in a full-grown specimen) ; the entire surface has fine striations, 

 which follow the direction of the costse. 



Specimens vary much in their length .and obliquity ; but none 

 are comparable to the Oxford Clay shell figured in the ' Illus- 



