43 
are about fifteen sulci on each side of the smooth central 
wave. A few lines of growth are marked on its surface, 
continuing over the back, which is finely striated longi- 
tudinally. The edges of the foramen are inflected. I 
have not discovered the spiral appendages to the hinge, 
but as they may be seen in Anomia trigonalis of Martin, 
t. 29. f. 36. it is probable they might be found in this, if 
the specimens were fortunately preserved. 
We were obliged to the late Mr. W. Martin for the first 
account of this species in 1798, and it had not been a se- 
cond time discovered by him or mentioned by any other 
author until very lately : he observes it is very rare at 
Castleton, and that its structure is truly remarkable, 
&c. As species of shells are said to determine the pre- 
cise age of the rock they are found in, by degrees we 
shall gain much useful instruction. 
A few years since my good friend, and friend to 
science, W. Danby, Esq. gave me a specimen, gathered 
below St. Vincent’s rock, near Bristol, and in May, 
1815, the Rev. J. M. Trahernes sent it to me as he ob- 
serves, “ from the Mountain Lime with Entrochi, near 
St. Hilary, Glamorganshire.” I have also a specimen 
from near Cork, by favour of Dr. T. Wood, in 1812. 
The two first have a few scaly remains of the shell ; they 
are somewhat distorted, with incurved beaks; that from 
Bristol has some signs of Entrochi, in a dark reddish 
Limestone ; in the other they are very distinct and abun- 
dant, the stone is darker with red stains. The specimen 
from Ireland has less of the shell, and is remarkably dis- 
torted, see fig. 5 ; this distortion appears to imply some 
difference in the age, as if a further change had taken 
place, which effected a total reduction or more total loss 
of the shell, softening the whole mass, the shell previously 
