130 EOCENE MOLLUSC A. 



A single specimen from the above locality is in Mr. Edwards's cabinet, and this I am 

 unable satisfactorily to assign to any other species. I therefore give it the above name 

 provisionally. The species this shell most nearly resembles is L. oblata, from Highgate, 

 but the present shell is thinner and flatter; it is also comparatively longer, and the 

 siphoni-lateral margin is more pointed. Our shell appears to be quite smooth upon the 

 exterior, and glossy ; the dorsal margin on the pedal side is slightly convex ; on the 

 siphon al side it is nearly straight. The specimen is firmly imbedded in the matrix. 



9. Leda substriata, Morris. Tab. XVII, fig. 5. 



Leda substriata. Morris. Geol. Journ., vol. viii, p. 266, pi. 16, fig. 7, 18.52. 



Spec. Char. L. testa minima, ovato-elongatd, subtrigond, tumidiusculd, sub-inrequi- 

 laterali, concent rice striata aid obtuse costatd ; pedi-regione ovato-rotundatd ; siphon i- 

 regione longiore, sub rost rata et sublcevigatd ; umbonibus prominulis ; lunula vix distinct 'd ; 

 ano elongato, lanceolato. 



Shell small, ovately elongate, obtusely trigonular, rather tumid, slightly inequilateral ; 

 concentrically striated or obtusely ridged ; pedilateral margin ovately rounded ; siphoni- 

 lateral obtusely pointed; beaks prominent; lunule ill defined. 



Length, |ths of an inch ; height, \ of an inch nearly. 



Localitg. Richborough (Prestioich) , Pegwell Bay {Edwards). 



"This shell, collected by Mr. Prestwich from the Thanet sands at Richborough, 

 Castle and Pegwell Bay, is difficult to distinguish from Nucula striata, Lam., which it 

 resembles in general form, but is rather longer in a transverse direction, and the stria? 

 differ a little, and are interrupted towards the posterior margin in some of the specimeus 

 examined." — Morris. 



In addition to the above remarks I may observe, that the Erench shell has different 

 proportions : the siphonal region is rather less than the pedal, whereas in the British shell 

 it is the reverse. This species appears still more to differ from Leda minima, which has a 

 distinct and well-marked anal or corselet region, with a defined and prominent ridge, 

 and the siphoni-lateral margin is in that shell more pointed than in either our present 

 species or the Erench shell L. striata. 



UNIO. Phillippson, 1788. 



Generic Character. Shell equivalve, inequilateral, generally thick and externally 

 smooth, occasionally corrugated or ornamented with nodules or spines ; aged specimens 

 sometimes become ponderous. Covered by an epidermis in the living state ; eroded at 

 the umbones; hinge with two short cardinal teeth in the left valve, and one, sometimes 

 two, in the right, and one elongated lateral tooth beneath the dorsal margin. Impressions 



