79 
PECTEN obsoletus. 
TAB DXLI. 
Spec. Char. Equivalved ; ears very unequal ; sur- 
face finely striated^ striae obliquely diverging. 
Ostrea obsoleta et O. laevis. Maton and Racket , 
Trans . Linn. Soc. 7. 100. 
var. cc . glabra; surface plairij sometime sulcated 
near the edge ; rarely marked with 4 or 
5 ribs. Figs. \, 2 , 3, 4. 
var. (3. sulcata : with many radiating sulci or 
deep striae^ surface often elevated in 4 
or 5 broad ribs. Figs. 5. 6, 7. 
var. y. costata ; surface elevated with from 7 to 
10 obscure ribs ; either plain or sulcated. 
Fig. 8. 
We have here grouped together a number of shells 
whose common characters are an equality and slight 
convexity of the valves, very small posterior ears, and 
minute arched striae diverging obliquely from an imagi- 
nary line drawn along the middle of each valve. We 
have divided them into three varieties; but the characters 
that have been selected to distinguish them are often so 
combined, that many more divisions might have been 
made, — a proof that they all belong to one species. The 
ears in all are alike strongly striated. Individuals of each 
variety occasionally occur with the margin for some 
breadth bent perpendicular to the surface (figs. 2, 3, 6 & 7): 
this circumstance is not so frequent ; nor are the ribs, 
when they occur, so strongly marked in the recent as in 
the fossil subjects ; otherwise there is not the shadow of 
a difference between them. 
Found abundantly in the Crag of Norfolk and Suffolk, 
by Mrs. Cobbold, the Rev. G. R. Leathes, &c. To the 
latter friend I am obliged for the use of the extensive 
series that has displayed the varieties so completely. 
This species resembles several upon plate 205 ; but 
they are a thicker shell, are more coarsely striated, and 
have larger posterior ears. 
