136 EOCENE MOLLUSCA. 



6. Unio tumescent, Edwards, MS. Tab. XX, fig. 17, a, b. 



Spec. Char. U. testa transversa, irregulariter oval a, tumidiusculd, valde iuaquilaterali, 

 laevigata ; pedi-regione convexd, siphoni-regione productd, subcuncatd ; umbonihus pro- 

 minulis ; lunula sub-excavatd ; cardine angusto, dente cardinali obtuso, dente laterali 

 elongate-. 



Shell transverse, irregularly ovate or ovately wedge-shaped, somewhat tumid, very 

 inequilateral; pedal region rounded, siphonal region produced; umbones slightly 

 prominent and rugose ; lunule shallow ; cardinal teeth obtuse, lateral tooth elongated and 

 narrow. 



Length, 1| inch. 



Localitg. Headon Hill {Edwards). 



A few specimens corresponding to the above characters are in Mr. Edwards's cabinet, 

 which he has considered to be distinct. I am unable to refer them to any published 

 species. 



7. Unio Vectensis, Edwards, MS. Tab. XX, fig. 15. 



Spec. Char. U. testa obtuse ovatd, vel ovato-rotundatd, injlatd, gibbosd, crassd, laevi- 

 gata ; umbonibus magnis, sub-prominulis ; pedi-regione rotundatd, siphoni-regionc 

 oblique truncatd vel obtuse angulatd ; margine dorsali convcxiusculd ; margine ventrali sub- 

 planatd. 



Shell obtusely ovate or ovately rounded, inflated, thick, smooth ; beaks slightly pro- 

 minent ; pedilateral margin rounded, siphonilateral obliquely truncated or sloping and 

 rounded ; pedal region one third the length of the shell ; dorsal margin convex ; ventral 

 margin slightly curved. 



Length, \\ inch; height, 1 inch. 



Localitg. Headon Hill, {Edwards). 



I have seen but one specimen, and this appears to be so very different in outline that, 

 with Mr. Edwards, I believe it to be quite distinct ; I have therefore adopted the' MS. 

 name he has given to it. 



Tab. XX, f. 19, represents a specimen of this genus from Headon Hill which I cannot 

 satisfactorily assign to any of the foregoing, or to any other species known to me ; at the 

 same time I am unwilling to consider it as entitled to a distinct specific position. I think 

 it possible it may be a distortion., and until better specimens be found it must remain 

 under the name of U. tumescens var. Headonensis. 



