129 



PECTEN sulcatas. 

 TAB. CCCXCIIL— F«^. 1. 



Spec. Char. Obliquely orbicular, with 20 

 obscurely tripartite rays, the intermediate 

 spaces longitudinally striated, the whole 

 rough with minute scales ; internally sul- 

 cated; ears nearly equal. 



Valtes nearly equal, convex, shorter than wide, with 20 

 rounding rays ; each ray is composed of ahout three scaly 

 ridges, and between each ray are several lesser, but 

 equally rough ridges , within are 20 furrows correspond- 

 ing to the external rays ; the margin is toothed. 



A common Crag Fossil, generally known by the name 

 of P. opercularis, although sufficiently distinct from the 

 recent species so called ; the internal furrows are a con- 

 spicuous character, besides which the striae upon the ribs 

 are sufficient to distinguish them. There is a species 

 from New South Wales more nearly allied, but in it the 

 spaces between the rays are flat, and transversely 

 striated, but not scaly. 



Very abundant in the loose Crag at Aldborough, but 

 rather scarce in the more compact Crag of Sudbourn, 

 and other parts of Suffislk. 



PECTEN gracilis. 

 TAB. CCCXCIU. —Jig. 2. 



Spec Char. Orbicular, thin, convex, with 

 many small, longitudinal ridges ; concentri- 

 cally striated ; striae close, elevated, sharp ; 

 ears unequal ; margin entire. 



liONGER than wide, every fourth ridge is rather more 

 elevated than the rest, and has an opposed grove within 

 the valve, that is much more conspicuous than those, 

 which, on account of the thinness of the shell, are 

 formed by the other ridges ; the strije are pretty uniform 

 over the surface, and not divided into scales, they are 

 however strongest near the margin. 



Two specimens, but of the same valve found in the 

 Crag near Ipswich, were formerly added to ray cabinet 

 of Fossils by Mrs. Cobbold, they are extremely fragile. 



