83 
UNIO, Lamarck • 
Mya^ Linn . 
Gen. Char. A transverse shell, having three mus- 
cular impressions, two very distinct and the 
third nearly united to the posterior one; an 
irregular callous hinge tooth, prolonging itself 
on the anterior side beneath the ligamental 
slope, and articulating with that of the op- 
posite valve. 
Several species of this genus abound in the Iron-stone 
stratum of Derbyshire, called the Muscle Band, and else- 
where, in the nodules found in what they call the 'Blue- 
bind, or in Bituminous Shale above the Coal, as on Lord 
Middleton’s estate at Woola ton in Nottinghamshire, 75 
yards below the surface; they are sometimes partially 
covered with Coaly matter, and often indicate Coal mea- 
sures. They are occasionally called Dog’s-tooth marble. 
UNIO subconstrictus. 
TAIL XXXIII.— Figs. 1, 2, and 3. 
Spec. Char. About twice as broad as long, with 
a constriction running from the front of the 
shell towards the beak on the anterior side, the 
end of which is subtruncated. 
Rather shallow, generally rather more than an inch 
broad, and half an inch long. 
Not a rare species, it was sent me from Derbyshire by 
Mr. Jonathan Salt; it is impressed upon a nodule of argil- 
laceous Iron-stone that has become ochraceous upon the 
exposed surface. Such Iron-stone is found to contain from 
#5 to SO per cent of Iron. There is a perforation in the 
shell, seemingly made by some species of worm. 
UNIO uniformis. 
TAB. XXXIIL— Fig. 4. 
My a ovalis, Martyn Petref . Derb. tab. 27. 28? 
Spec. Char. Subovate, beak near the middle of 
the shell, anterior and posterior ends elliptical 
W idth nearly twice as much as the length ; rather deeper 
than the last, and differs also in having the beak nearer the 
