212 
a-HE GEOLOGIST. 
with vegetable remains ; but on driving the gallery eastward the 
conglomerate became regularly bedded, and attained a maximum 
thickness of four feet, made up plentifully of the shells of Cyrena 
cuneiform is, C. cordata, G. Duhvichiensis, Melania inquinata, and the 
new genus Pitharella, now figui'ed and described by Mr. Edwards. 
I aiinex a description of the distinguishing generic characteristics of 
the Cijrena Duhvicldensis, and, as an accompaniment to the figure, 
some of the prominent peculiarities noticeable in the species. 
Cyrena Dulwichiensis (Rickman) : Spec. char. — Shell elongately 
oval, transverse, inequilateral, posteriorly shghtly produced, and 
obscurely truncated ; umbones prominent, tumid, cunred ; lunule 
large, and of an oblong oval form. The anterior extremity presents 
on the surface numerous irregular and rather deep concentric 
furrows, which become shallower as they cross the middle, and 
almost obsolete over the posterior extremity. The shell is orna- 
paented with irregular longitudinal bands or y&js of colour, usually 
eight to ten on each valve, but varying in number and breadth in 
different specimens. The shelly matter forming the coloured surface 
of these bands appears to have been particularly susceptible of dis- 
integration, for most generally it is foiind to have been decomposed, 
leaving a perceptible furrow, corresponding with the ray, impressed 
on the surface. The hinge lamina is much curved, and has three 
divergent cardinal teeth, of which the central one is slightly bifid, 
and two unequal, compressed, lamelliform lateral teeth, strong]}'' 
serrated. 
Size. — Length, 2 inches and l-12th ; height, 1 inch and 6-12ths. 
Explanation of Plate V. 
Fig. 4. — Cyrena Dulwichiensis. Pig. 5. — Interior of valve, showing the hinge 
and muscular impressions. Prom specimens in the collection of F. E. Ed- 
wards, Esq. 
