41 
SPIRIFER. 
Gen. Char. An equilateral unequalvalved bivalve ; 
valves beaked ; one valve with a large angular 
sinus along the inside of the beak ; hinge 
transverse, long and straight. Two spirally 
coiled linear appendages to the hinge nearly 
filling the shell. 
The shells of this Genus are in general wider than long, 
with a large sinus or fold elevating the front ; unarmed ; 
many of them longitudinally furrowed. The sinus in 
the beak being met at its open end by the back of the 
lesser valve, forms a triangular foramen, with inflected 
edges.* The surface of the beak on each side of this fora- 
men is flatted and often widely extended, having numerous 
parallel longitudinal strise upon it, which gives it much the 
appearance of the outside of the hinge of Area. I think this 
Genus will comprehend nearly all the shells, retained as 
Terebratula by Lamarck, which have a triangular foramen 
and not a perforation at the apex of the beak as the cha- 
racter of that Genus requires. The several individuals in 
which I have discovered the spiral appendages, bear a con- 
siderable natural affinity to each other, f from which circum- 
stance we may venture to place many analogous species 
in the Genus, although their interior has not been ex- 
* In some species I have traced these edges quite across the beak, forming 
septa, somewhat like those in the flatter valve of the Pentamerus, but 
confined to the beak. 
f I gave a paper some time since to the Linnean Society, on the con- 
struction of this spiral tubular cartilage, which almost fills the shells, 
and which I have seen full proof of in Derbyshire and Irish specimens; 
and Mr. Brown has some curious specimens from Van Diemens iand. 
