BIVALVIA. 31 
Prcren ricipus, Sow. Tab. XL, fig. 16. 
PEcTEN RIGIDUS, Sow. Min. Con., t. 205, fig. 8. 
— _— Morris. Catal., 1854, p. 177. 
— — D’Orb. Prodr. Et., xi, p. 314. 
-— — Oppel. Juraformation, p. 492. 
Testa ovato-orbiculari, sub-equivalvi, plano-conveea, reticulata, costis depressis, crebis, 
sub-regularibus, divergentibus, lamellis concentricis angustis, hinc inde decussatis; auri- 
culis inequalibus, transverse lamellosis, lamellis elevatis, crebris. 
Shell ovately orbicular, equivalve or subequivalve, moderately convex ; cost diverging, 
depressed, slightly unequal, sometimes undulating and closely arranged, crossed by narrow, 
irregular, concentric lamella, which are sometimes elevated upon the ribs, and in other 
instances form only narrow lines across the interstitial spaces, giving to them a punctated 
aspect ; auricles large, unequal, with numerous transverse, narrow, elevated Jamellz. 
Geological Positions and Localities. It is not uncommon in the upper portion of the 
Great Oolite, in the Forest Marble, and in the Cornbrash of many localities, as at Castle 
Combe ; Stanton, near Chippenham ; Kidlington, Oxon.; Rushden, Northamptonshire ; 
Luc, France. 
Pecten Griessacut, Lyc. Tab. XX XIII, figs. 6, 6 a. 
Testa, valva sinistra crassa subequilaterali acuta, compressa, auriculis magnis sub- 
aequalibus, radiatim costata et concentricé striata, costis (circa 26) superne angustis sub- 
equalibus transverse striatis, inferne obsoletis ; striis concentricis, regularibus tenuissimis ; 
auriculis transverse plicatis. Valva altera compressa interne levigata. 
Shell with the left valve thick, subequilateral, compressed, acute; auricles large, nearly 
equal, and transversely plicated; the surface is ornamented with about twenty-six very 
delicate, radiating costa, which are striated, narrow, nearly equal, and regular; they are 
distinct towards the apex, but are only faintly traced towards the middle and lower part 
of the valve; the concentric striations are very fine and regular over the whole surface; 
a few faintly marked plications of growth are visible towards the lower border. ‘The 
external surface of the right valve has not been exposed; its convexity is about equal to 
that of the other, its mner surface being smooth, without traces of the exterior orna- 
mentation. 
Geological Position and Locality. The Great Oolite of Wollaston, Northampton- 
shire, in the cabinet of the Rev. A. W. Griesbach. 
