123 
UNIO L isteri. 
TAB. CLIV. — Fig. 1, 3, and 4. 
Spec. Char. Cordate, transversely imbricated, 
beak recurved, acute; posterior side small; 
middle flattish ; shell thick. 
1 he front of this species is sharper or more wedge- 
shaped than is usual in shells of this Genus ; neither the 
posterior side nor the cartilage slope are so round as ill 
Unio crassissimus : £he breadth is but very little greater 
than the length. 
This always puts me in mind of Lister’s “ Musculus 
fluviatilis e jluvio Thamesi ad Battersea ” tab. 184, and the 
varieties of Unio ovata in part corresponding with his fi- 
gure and which I find occasionally at the same place, 
wherefore I have named it after him. Fig. 1 was sent 
me from Durham, as found in that neighbourhood some 
years since in Clayey Limestone : it accords much with 
some smaller mutilated specimens from Suffolk, by favour 
of Dawson Turner, Esq. and from an etching by favour 
of Mr, Richard Taylor, it appears to be found in Roydon 
gravel pit, near Diss, in Norfolk, rather more perfect and 
plentiful : but if the same species they differ a little in the 
state of preservation, being apparently less smooth, and 
formed of a lighter coloured Carbonate of Lime. 
The specimens, fig. 3 and 4, are from Scarborough ; 
the smallest is a young shell before it has acquired its 
cordate form, from my friend Mr. Strangewayes, who 
found several specimens there ; the other I bought of a 
dealer from thence. Perhaps this is the “ thick ovate 
shell, a little depressed, found at Malton and S earner 
quarries, in length two inches and a half, in breadth three 
inches;” mentioned in Scarborough Fossils, p. 103, 
where it is put under the Genus Tellina, 
