BIVALVIA. 135 



size, deeply impressed, and there is a distinct pedal one within and a little below it ; the 

 anal one large and remote ; the umbones are rugose, and generally eroded. The epidermis 

 is visible on well-preserved specimens, which have also the connector entire, extending from 

 the umbo about half the length of the shell. 



A large portion of the stratum in which these shells abound at Hordwell is a marly 

 bed, but I obtained a few perfect specimens from a pure siliceous sand. 



5. Unto subparallela, Edwards, MS. Tab. XX, fig. 13, a, b. 



Unio Deshayesii ? Prestvnch. Quart. Journ. Geol. Soc, 1854, p. 118. 



Spec. Char. U. testa elongatd, sub-quadrangidald pel ovato-oblongd, laevigata., depressd, 

 valde inaquilaterali ; pedi-regione brevi, rotundatd ; siphoni-regione longiore, sitbangulatd 

 vel oblique truncatd ; umbonibus depressis ; marginibus ven trail et dorsali subparallelis. 



Shell transversely elongate, or ovately oblong, smooth, depressed, very inequilateral ; 

 pedilateral margin rounded ; siphonal region much the larger, slightly angulated or 

 obliquely trunculated ; umbones depressed ; dorsal and ventral margins nearly parallel ; 

 ventral margin slightly incurved. 



Length, 2\ inches; height, jfths of an inch. 



Localities. Peckham {Edwards), Counter Hill, Deptford (Preslwich). 



The specimen referred to U. Deshayesii by Mr. Prestwich most probably belongs to the 

 same species as the one here figured, but " its mutilated condition would not permit of 

 determination." 



In comparing our present species with the U. Wateleti (olim U. Deshagesii), the 

 differences appear too great to permit of their being united, and I have therefore adopted 

 the MS. name that was attached to Mr. Edwards's specimen. 



I am the more disposed to this separation, because I have not only the figures 

 and description of the French shell in the valuable work by M. Deshayes, but there is also 

 a specimen in the cabinet of Mr. Edwards, sent from France by the author of the species. 



A shell from the " Terrain de lignite " in the South of France has been figured and de- 

 scribed by M. Matheron under the name of Unio galloprovincialis; 'Cat. raeth. et descr. des 

 corps organ, foss. des Bouches du Rhone,' p. 168, PI. 23, fig. 1, which appears from 

 representation very closely to resemble our own, and when the specimens themselves can 

 be compared, may probably be found to belong to the same species. The only difference 

 I can observe on comparing the figure is that the umbo of the French fossil is rather the 

 more prominent of the two. 



