145 
PECTEN duplicates. 
TAB. BLXXV.— figs. 1. 2. &3. 
Spec. Char. Orbicular, depressed, radiated ; one 
valve nearly smooth, the other very rough and 
ornamented with many distant, thin, round 
ribs, which become more numerous towards 
the margin ; ears defined, small. 
One of the valves has the surface covered with minute 
sharp scales; the other is smooth and almost free from 
ribs, being only undulated in their places : this is the 
most convex, the inside of both valves is nearly plain. 
Near the beak the ribs are about ten ; but at the margin 
there are forty, in consequence of the interposition of 
new ones as the shell increases in size. 
First found 200 feet from the surface in a well dug in 
London Clay on the top of the hill in Richmond Park. 
See fig. 3. In Hyde Park it has been found whenever 
the Clay has been exposed. The specimen delineated at 
figs. 1. and 2. was kindly given me by Mr. Marshal, who 
collected several last year. 
PECTEN carinatus. 
TAB. BLXXV.— -fig. 4. 
Spec. Char. Orbicular, rather elongated, convex, 
smooth, ribbed ; ribs about seventeen, distant, 
rounded, with a sharp keel along the middle 
of each ; ears defined, rather large ; internally 
sulcated. 
Between each of the broad carinated ribs is an equally 
broad flat smooth space, along whose middle there ge- 
nerally runs a sharp line : the ears are square and am- 
ple ; the valves are equally convex. / 
Found in Barton Cliff, and also in other parts of 
Hampshire. 
