BIVALVE SHELLS. 233 



No. 9 agrees with the p. varius, having unequal ears, and 

 between twenty and thirty spinous imbricated ribs. The ribs vary in 

 number, especially as we often see two ribs coalescing into one, or 

 one dividing into two ; as may be observed also in the very correct 

 figure of the recent shell in Pennant's Zoology, IV. PI. LXI. This 

 shell, which measures two inches or more in length, and somewhat 

 less in breadth, is found in the oolite near Malton. In the same 

 place, we meet with a shell greatly resembling it in form and size, 

 but with only about eighteen ribs, and these not spinous, but trans- 

 versely wrinkled, and sometimes rather scaly. It appears to be p. 

 citrinus, or a variety of p. senatorius. In the oolite we also find a 

 pecten, sometimes three inches long or upwards, having ten large 

 ribs, with imbricated transverse strise. The ribs appear to have been 

 somewhat prickly, and the shell is perhaps allied to p. sanguinolenttis 

 (or ostrea sanguinolenta ) ; but our specimens of it are all imperfect. 



No. 3 is a perfect valve of a beautiful little pecten, very common 

 in the oolite, and in the calcareous sandstone under it. We may 

 term it p. sulcatus, as it corresponds very nearly with Dill wyn's o«^rm 

 sulcata ; having eleven or twelve prominent ribs, traversed by sharp 

 scales, or oblong spines. The grooves between the ribs ai'e faintly 

 marked with transverse striae, connecting the scales that cross the 

 ribs. Only a few longitudinal striae are discernible, so that the 

 shell differs a little from o. sulcata. 



No. 12 is about the same size as No. 3, each of them being 

 nearly an inch long. They have also the same number of ribs ; but 

 those of No 12, which is a wider shell, are rather broader and flatter; 

 and instead of sharp scales, are traversed by slender undulating 

 membranaceous striae, which cross the grooves as well as the ribs, 

 and are so closely set as nearly to cover the whole shell. This 

 seems to be the p. fibrosus of Sowerby, Tab. 136. Fig. 2; and it is 

 probably allied to the ostrea striatula of Linnaeus, which has sixteen 



3 M 



