91 
LUTRARIA, Lamarcke. 
MACTRAj Linn. 
Gen. Char. A transverse, inequilateral bivalve., 
gaping at the extremities; two oblique and 
diverging hinge teeth, one on each side of a 
large pit for the cartilage. No lateral teeth. 
MACTRA gibbosa. 
TAB. XLII. 
Spec. Char. Gibbose, anterior side much wider 
than the posterior, recurved, truncated, gaping. 
Jjength and depth about equal; breadth equal to twice 
the length : the posterior side is rounding and about one- 
third the breadth of the other; beaks much incurved and 
pointed. 
This fine specimen is from the great Oolite Limestone 
stratum, near Bath. I am favoured with it by the Rev. 
H. Steinhaiier. The external characters when compared 
with those of Mactra hians agree in every particular, but 
that it has more gibbosity and a boldness of feature in the 
curve and beak, conveying the idea of an extravagant 
variety, yet too strongly marked to allow a doubt of its 
being specifically different. This analogy gives a full 
sanction to its being considered as an undoubted Mactra of 
