MARSHALL: ADDITIONS TO ‘‘ BRITISH CONCHOLOGY.” 387 
and figure in Sowerby’s Index, and the name is a very 
appropriate one. It is not described in “British Mollusca,” 
but the authors say in their Supplement :—‘ We have two 
distinct forms, the broad [long] one as figured, and an 
elongated [short] variety which approaches Z. od/onga. 
In the former, the dorsal edges are usually more convex 
and have a greater declination than in the latter, where 
they are more or less retuse towards the beaks.” This 
variety is smaller, narrower, and more slender, the 
front and back margins are almost parallel except for a 
shallow sinuation in the centre of the lower margin, as in 
Unio margaritacea; the umbones are more prominent, 
the posterior gape wider, and it is more truncate at that 
end. L. 2, B. 4. The young of all sizes partake of the 
same characters as the adult. I have found it at Jersey 
and Herm, where it is the normal form, living with Z. 
oblonga in sand at very low tides ; it also occurs occasion- 
ally with the type in Torbay and a few other places. Var. 
intermedia is figured in Sowerby’s Index (fig. 1) as the 
type ; but fig. 2 1s the type form ; and it is well figured in 
Brown’s Illustrated Recent Conchology. <A valve is also 
figured by Searles Wood from the Coralline crag, to which 
valve Jeffreys had written under the tablet “ Z. od/onga,” 
but Wood says he considers it a variety of Z. e//iptica, and 
that it resembles a figure by Dr. Hornes of a variety of Z. 
oblonga, but which is also figured by Mayer as a distinct 
species, Z. Aornestt. Wood’s figure exactly represents this 
variety. 
L. oblonga Chem. lives with Z. e//ptica Lamk., at Herm and 
Jersey ; but while in the former island the proportions are 
one L. oblonga to forty L. e/liptica, at Jersey these propor- 
tions are reversed, and Z. ob/onga is the common form. 
Both species are subject to the same inconvenience from 
sand, as mentioned in the case of Mactra stultorum, and Dr. 
Jeffreys’ “ curious malformation, the specimen having an 
