212 



THE GEOLOGIST. 



with vegetable remains ; but on driving tbe gallery eastward the 

 conglomerate became regularly bedded, and attained a maximum 

 thickness of four feet, made up plentifully of the shells of Cijrena 

 cuneiformis, C. cordata, G. DulivicMensis, Melania inqidnoia, and the 

 r.ew genus Pitharella, now figured and described by Mr. Edwards. 

 I annex a description of the distinguishing generic characteristics of 

 the Cyrena Dulwicliiensis, and, as an accompaniment to the figure, 

 some of the prominent peculiarities noticeable in the species. 



Cyrena Dulivichiemis (Rickman) : Spec. char. — Shell elongately 

 oval, transverse, inequilateral, posteriorly slightly produced, and 

 obscurely truncated ; umbones prominent, tumid, curved ; 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- 

 mented with irregular longitudinal bands or rays of colom', usually 

 eight to ten on each valve, but varying in number and breadth in 

 difierent 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 found to have been decomposed, 

 leaving a perceptible furrow, corresponding with the ray, impressed 

 on the sm-face. The hinge lamina is much curved, and has three 

 divergent cardinal teeth, of which the central one is slightly bifid, 

 and two unequal, compressed, lameUifonn lateral teeth, strongly 

 serrated. 



Size. — Length, 2 inches and l-12th ; height, 1 inch and 5-12tlis. 



EXPLAXATIOX OF PlATE Y. 



Fig. 4. — Cyrena Duwichiensis. Fig. 5. — Interior of valve, sliowing tlie liinge 

 and mnscuiar impressions. From specimens in the collection of F. E. Ed- 

 wards, Esq. 



