BIVALVIA. 31 



Pecten rigidus, 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 ovafo-orbiculari, sub-aquivalvi, plano-convexa, reticulata^ costis depressis, crebis, 

 sub-re^ularibus, divergentibus, lamellis concentricis angustis, kinc inde decussatis ; auri- 

 culis inaequalibus, transverse lamellosis, lamellis elevatis, crebris. 



Shell ovately orbicular, equivalve or subequivalve, moderately convex ; costse diverging, 

 depressed, slightly unequal, sometimes undulating and closely arranged, crossed by narrow, 

 irregular, concentric lamellae, 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 lamellae. 



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 ; KidHngton, Oxon. ; Rushden, Northamptonshire ; 

 Luc, France. 



Pecten Griesbachi, Lye. Tab. XXXIII, figs, 6, 6 a. 



Testa, valva sinistra crassa subaequilaterali acuta, compressd, auriculis magnis sub- 

 cBqualibus, radiatim costata et concentrice striata, costis {circa 26) superne angustis sub- 

 cequalibiis transverse striatis, inferne obsoletis ; striis concentricis, regularibus tenuissimis ; 

 auriculis transverse plicatis. Valva altera compressa interne lavigata. 



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 costae, 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 inner 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. 



