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 mequality 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 coste, regular in 
the young shell, subsequently degenerating into irregular and 
unequal elevations, more especially when the surface exhibits 
arrests of growth; the costz 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 costz. 
Specimens vary much in their length and obliquity ; but none 
are comparable to the Oxford Clay shell figured in the ‘ Illus- 
