83 
PECTEN equivalvis. 
TAB. CXXXVL —Fig. l. 
Spec. Char. Lenticular, with rounded diverging 
ribs and many acute concentric striae ; valves 
equally convex, the lower one smoothest ; ears 
equal. 
The ribs vary in proportion ; they sometimes equal the 
space between them, but are generally less; they are 
rounded and the striae are more or less obliterated over 
them : the spaces between them are slightly concave. 
Pectens are generically described by Lamarck as in- 
equivalve, wherefore, I suppose, he had not seen any 
otherwise ; but the present species has both valves nearly, 
if not quite, equally gibbous : one valve being simply 
convex, the other having a trifling reversed undulation 
near the edge, and differing but little in the pattern. The 
auricles have not, as I have seen, been found perfect, 
they are, however, nearly so, and they then show an 
horizontal line on each side of the beak, with nearly per- 
pendicular line® or striae. I have one by favour of Dr. 
Sutton, which has nearly parallel lines with the hinge on 
the dexter auricle of the broader valve, with the broad 
costae. This species is commonly found from three to 
seven inches in diameter. Mr. S trail gewayes, from whom 
I have received several specimens, observes, that they 
are characteristic of the coarse Limestone of Ilminster. 
I have had other specimens from near Lackington, by 
favour of Mr. Strangewayes, also from Farley gateway, 
Gloucestershire ; Carrington, Oxfordshire ; and from 
Dursley, Gloucestershire. I believe tho species is found 
in various other parts of England, and I have a specimen 
from France. 
